Presuming that those who originally responded to this post long ago are still of the same opinion, I will offer the following observations to counter the late-date arguments. My preference is to rely on evidence from within Revelation and scripture itself, since this should supersede all other methods of proving something. Many of these points I have brought up before on this site from time to time, but this will put a group of them in one location for reference.
Revelation written before AD 66:
#1) Revelation 17:18 tells us that, at the time John was writing, "that great city...RULETH (present tense) over the kings of the earth". This phrase, "kings of the earth" is not the same thing as the "kings of the whole world", because Revelation 16:14 mentions both of these as distinct from one another. "Kings of the earth", according to how Christ presents them in Matthew 17:25, were the HIGH PRIESTS OF THE LAND OF ISRAEL. These "kings" / high priests were being ruled over by "that great city" (Rome-governed Jerusalem) as John was writing.
It does not take a master's degree to figure out that there are NO HIGH PRIESTS in existence anymore being ruled over by "that great city" of Jerusalem (or any other great city for that matter), and haven't been ever since the AD 66 Zealot uprising when the Jews cast off the yoke of Roman governance in Jerusalem at the start of the Roman / Jewish war. After that, all physical genealogical records that could have ever re-established any kind of high priest according to Mosaic law were burned up in the AD 70 demolition of the temple. So, Revelation had to have been written at least before AD 66, when the high priests were still in subjugation to "that great city" Jerusalem, which had the high priesthood under its thumb in cooperation with the Roman authorities.
Revelation written before AD 70:
#2) There absolutely WERE false prophets and false messiahs that abounded in the pre-AD 70 era. Christ had predicted in Matthew 24:24 that these would arise in the generation He was speaking to. Some of these false messiahs would be rumored to be in the "secret chambers" (Matt. 24:26). This is a reference to "The Chamber of Secrets" in THE TEMPLE THEN STANDING, which was a repository where donations for the poor in Israel could be given and then dispensed anonymously in those days. This temple was crushed at the close of AD 70, so there is no way possible that these false messiahs would be rumored to be in "The Chamber of Secrets" after those chambers were destroyed along with the temple in AD 70.
Revelation 11:1-2 is a text where John is told to measure that existing temple, the altar, and those who worshipped in it. To measure something in scripture typically means that it is preserved for a period of time - in this case for 42 months while the Gentiles trampled the city and the outer temple court underfoot (mainly the Zealots coming from "Galilee of the Gentiles"). If John had been writing Revelation in AD 95 or thereabouts, there would have been no point for him to measure a temple for a 42-month period of preservation if that temple had already been demolished 25 years previously.
Revelation written before AD 70:
#3) When John was writing Revelation, he was not describing the Bar Kokhba revolt - he was predicting the time and events that would occur when the "POWER of the holy people" would be shattered, as Daniel 12:7 mentions. This "power" of the holy people was not referring to Israel's military strength, its wealth, or status as a nation. Daniel defines his own terms of what this "POWER" was.
In Daniel 11:31, when he was prophesying about the profane actions of Antiochus polluting the temple with the "abomination that maketh desolate", Antiochus was predicted to "pollute the sanctuary of STRENGTH", and to take away the daily sacrifice. This "sanctuary of STRENGTH" was the temple itself that Antiochus Epiphanes desecrated. The temple was the "power of the holy people" - the nerve center, and the heart and soul of Judaism. Once this "power" was shattered in AD 70, "all things" prophesied in Daniel were "finished" (Daniel 12:7). This negates any importance given to the fall of Masada later on in AD 73, or to the AD 132 Bar Kokhba revolt. Neither of those events had any significance after the "POWER" of the "sanctuary of strength" - the temple - was shattered in AD 70.
All those fulfiled prophesies of Daniel included a resurrection (Daniel 12:1-4) and the unequaled Great Tribulation time of trouble at the "time of the end". What the angel with hands raised to heaven swore would happen, but wanted "sealed" until the "time of the end" was unsealed in Revelation. The next time we see a mighty angel raising his hand to heaven and swearing by God who lives for ever and ever, he declares that "there shall be no more delay", but that the "mystery of God" would be FINISHED as soon as the 7th angel sounded. This "mystery of God" was revealed to us by Paul - that in Christ, the believing Gentiles should partake of the same promise and be fellow-heirs with the believing Jews in a shared inheritance of a resurrected body.
Revelation written before AD 67:
#4) Those adherents of the "doctrine of Balaam" which had infiltrated two out of the seven churches in Revelation 2 & 3 were given a promise by God that, if they did not repent of their deeds, He would cast them into Great Tribulation and kill with death those "children" who were following the leader of this cult. This promise of judgment to come on the "doctrine of Balaam" followers was a judgment they were "ABOUT TO RECEIVE" in II Peter 2:13. This means Revelation was written PRIOR TO II Peter (which was written just before Peter's martyrdom in AD 67 - II Peter 2:14-15).
Revelation written before AD 60:
#5) The Laodicean church in Revelation 3:14-16 was warned by God that "I AM ABOUT TO SPUE YOU OUT OF MY MOUTH..." because they had developed into an overconfident, self-satisfied congregation. We know from multiple records of historians during this period that the city of Laodicea was devastated by an earthquake in AD 60, which would indicate that this disaster was the fulfillment of God's promise to spue them out of His mouth if they did not repent. This would therefore indicate a pre-AD 60 date for Revelation's composition.
Revelation written before AD 67:
#6) Revelation had a total of seven churches in Asia that it addressed in John's days. A total of five out of these seven were warned to "repent of their deeds". Switch over to Paul's letter to Timothy in II Timothy 1:15. It says, "This thou knowest, that ALL THEY WHICH ARE IN ASIA be turned away from me;" This shows that by that time, the total number of churches in Asia had defected from supporting Paul, which means that all seven churches in Revelation had succumbed to pressure against the faith. If these Asian churches were still in a wavering condition that had not quite fallen yet in Revelation, this means Revelation had to have been written BEFORE II Timothy (which was written just before Paul's martyrdom in June AD 67 - II Timothy 4:6).
Just as Paul had announced that a massive defection from his teaching had occurred in Asia, Revelation predicted that the kingdom of the Sea Beast in ASIA would be "darkened". Revelation 16:10 tells us that the 5th angel poured out his vial on "the SEAT of the Beast" and his kingdom was "darkened" when those in that kingdom "repented not of their deeds". This "SEAT of the Beast" was given to it by the Dragon in Revelation 13:2, which "SEAT" of the Dragon was originally in Pergamos of Asia, where Satan dwelled (Rev. 2:13). So, the kingdom of the Sea Beast in Asia was "darkened" when the seven churches ended up distancing themselves from Paul in order to protect themselves from persecution. What was predicted EARLIER in Revelation 16:10 finally came true LATER in II Timothy 1:15, just before AD 67.
Revelation written before AD 60:
#7) The faithful in the church of Smyrna in Revelation 2:10 were told not to fear any of those things that they were ABOUT TO SUFFER. They were told that Satan was ABOUT TO CAST some of them into prison. They would then have tribulation for "TEN DAYS". This did not last for ten literal 24-hour days, anymore than it took a literal "one hour" for Babylon to fall in Revelation 18:10, 17. This is probably 10 YEARS being predicted. If Revelation was written just before the AD 60 Laodicean earthquake, then the soon-coming TEN YEARS of persecution for the faithful in Smyrna would last from AD 60 until AD 70, when those faithful Smyrna believers who had died would be given a "crown of life" in the AD 70 bodily resurrection.
Revelation written before AD 63:
#8) The "seven kings" from Revelation 17:10 that are presented as part of the Scarlet Beast in the wilderness I have spoken about before on this site as being the seven high priest "kings of the earth" that were from the house of Annas. Their terms of service in the office of high priest and the years they served match perfectly with the language in Revelation 17:10-11, as follows.
"Five are fallen" (because Annas and four of his high priest sons had died by the time John wrote Revelation) "and one is" (Matthias was one son of Annas that was still alive then) "and the other IS NOT YET COME" (into the office of high priest) "and when he cometh, he must continue a short space" (because Ananus, son of Annas, after three short months of service in AD 63 was deposed from office for the offense of instigating the murder of James the Just, Christ's half brother).
"And the beast that WAS" (the independent kingdom of Israel that lasted for about 80 years after the Maccabean victories) "and IS NOT" (because this independent kingdom of Israel was subjugated by Pompey in 63 BC) "even he is an eighth, and is of the seven" (because the eighth high priest, Annas' grandson Mattathias, was in the genetic line of the other seven high priest "kings", and would become the high priest leader in AD 65-66, when the Scarlet Beast's independent kingdom of Israel came into existence once more) "and goeth into perdition" (because the eighth high priest "king" would be killed in AD 66, and also the Scarlet Beast itself - which was ABOUT TO arise from the abyss when John was writing as Rev. 17:8 tells us - would also go into destruction when Jerusalem fell in AD 70.)
All this tells us that Revelation was written at least sometime before Ananus, the seventh "king" / high priest took office in AD 63.
Revelation written between late AD 59 and AD 60:
#9) In Revelation 1:9, John said that he was then a "companion in tribulation" with those brothers he was writing to. This "tribulation" John was sharing is not to be confused with the Great Tribulation that God promised to send later (Revelation 2:22). The tribulation John was then experiencing was the persecution that followed after the initial outbreak against Paul - the riot started by the Ephesian silversmiths in AD 59 (Acts 19:23-41), which the hostile Jews took advantage of to persecute Paul afterward (Acts 21:27 and following). This persecution by the Jews grew into violent hatred against Paul and those who followed his teaching in the Asian churches.
Ephesus was the capitol of Asia, and once persecution launched against Christians in this city, it spread throughout Asia. This is why Smyrna, some 30 miles or so away from Ephesus, was ABOUT TO experience persecution for "TEN DAYS", or ten years in Revelation 2:10. In addition, the Isle of Patmos was under the jurisdiction of Ephesus, so if the disciples had to leave Ephesus, or were banished from Ephesus, the logical place for John to be sent shortly after the silversmiths' riot in AD 59 was to the Isle of Patmos, just off the coast of Ephesus. This is when he penned the Revelation to his brothers and companions in tribulation in the seven Asian churches.
I could also add to the list above other external evidence we have proving that John was on Patmos during Nero's reign, but I have posted that elsewhere on this site before.
I could also counter the misunderstanding of Irenaeus' one statement that is presumed to prove a late date for Revelation. This piece of external evidence is a weak case indeed to prove anything, considering that this late-date "proof" is based on a single word that has been inserted into the translation of Irenaeus' statement at the discretion of the scribe who did the translating. It is not based on anything that Irenaeus himself actually wrote.
Just for kicks and grins, I could also submit the external evidence found in my Cambridge King James Bible in its Bible dictionary in the back. Under the definition for the "Revelation of John", it includes the following statements: "There is a considerable difference of opinion as to the date of its composition. One tradition states it to have been written at the end of the reign of Domitian, about A.D. 96, while another connects it with the persecution of Nero, A.D. 64-8. THE EARLIER DATE IS THE MORE PROBABLE....Also the interpretation of the Rev. is easier if it belongs to the period just preceding the downfall of Jerusalem, and refers to events which lay in the immediate future."