We have been through this so many times. Death is used in at least three different ways. The first is physical death, the death of the physical body. The second is spiritual death. It s the state of corruption of the spirit of man once he has committed sin. Unless corrected through being in Christ it leads to the third death. The third death is eternal death. It is the eternal separation of the spirit from God following the final judgment, i.e., hell. In order to make sense of any of the Scriptures speaking about death, it is necessary to understand which death is in view.
Relative to Romans 5:12, it is spiritual death which ENTERED due to Adam. Physical death entered the world with the creation. There is no such thing as physical immortality. Not even the Universe was created to exist forever.
As far as your seeing no exception to the "all" that have sinned, certainly Jesus was a man who did not sin, and exception. And if you understand what is sin you will understand why, by definition, those incapable of understanding the law and the consequences of disobeying the law have not sinned. And once you rid yourself to the concept of the false doctrine of original sin that will become even more apparent.
Let's take a look then if the death mentioned in Rom. 5:12 is what you say as spiritual death and not physical death.
12 Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned:
13 (For until the law sin was in the world: but sin is not imputed when there is no law.
14 Nevertheless death reigned from Adam to Moses, even over them that had not sinned after the similitude of Adam's transgression, who is the figure of him that was to come.
You said "Relative to Romans 5:12, it is spiritual death...". That makes it saying that spiritual death passed upon all men. Still that does not except anyone. That would include then babes, little children, and mentally deficient men. That makes all men spiritually dead. Now, you said spiritual death is the state of corruption of the spirit of man once he has committed sin. Yet, the verse says "death passed upon all men".
Some might argue that the last part "for that all have sinned", which is the reason why "death passed upon all men", tells us that death, which in your take is spiritual death, is only passed to those who have sinned. By itself, the phrase "for that all have sinned" is clear, and without exception. Nonetheless, granting for the sake of argument, that only those who have sinned are spiritually dead, we move on to what it makes of v.13 & 14. In v. 13, Paul laid the fact that sin is not imputed when there is no law. So, when there is no law, sin is not imputed to any man, which makes him not spiritually dead, but spiritually alive ~ with an uncorrupted spirit as opposite to your take of spiritual death. Considering the men who lived in the period from Adam to Moses, when there was no law yet given, they would not then be spiritually dead, for sin is not imputed when there is no law. The question is, were they not spiritually dead? Evidently they were, which then contradicts your position that "spiritual death is the state of corruption of the spirit of man once he has committed sin". Now, Paul also laid out the fact that sin was in the world, even until the law was given, the period being from Adam to Moses, which all the more makes such take that death is spiritual death to be wrong, as it will render the phrase "sin is not imputed when there is no law" as false.
In v.14, Paul speaks of death as to reign. The word "Nevertheless" has significance here in connection to death's reign. It connects what is said in v.14 to what was said in v.13. That despite the fact that sin is not imputed when there is no law, death reigned over men, even at the time from Adam to Moses, when no law was yet given. The relative point in this then is that spiritual death exist and has dominion over those who lived at the time of Adam to Moses. Now, the verse goes on to say "even over them that had not sinned after the similitude of Adam's transgression". That clearly contradicts your position that "spiritual death is the state of corruption of the spirit of man once he has committed sin".
This clearly mess up what Paul was saying in the passage. It would not make much sense.
None of that really matters. Because verses 18 &19 says that whatever you thought came to mankind due to the one transgression of Adam, it was negated completely by the one act of obedience of Jesus. Original sin whatever you think of it is simply not true; it is false.
Apparently, there is no counter explanation in defense of your position that the death spoken of in Rom. 5:12 refer to spiritual death.
Perhaps, you have a point in saying that the issue at hand does not really matter because of Christ. But why say that now, when you have, in a great extent, discussed your thoughts on it? Perhaps because, such matter really does matter. Afterall, this is scriptures ~ God's words, which affects the very mind, heart, and soul of man which relates to his Creator.