As he himself says in Romans chapter 11 verse 13 that he is the Apostle of the Gentiles. So, as Gentiles, naturally, he is the one to whom we should turn for our basic doctrines. Verse 12:
Romans 5:12a
"Wherefore, as by one man (he is referring to whom? Adam.) sin entered into the world, and death (let me use the verb, entered) by sin; (in other words, before Adam ate, nothing died. Death was an unknown entity. But, once he ate, sin came in and with sin came death.) and so death passed upon (how many?) all men,..."
ALL, Paul says in Romans chapter 3 -- ALL have sinned and come short of the glory of God. No one escapes it because we have been born of Adam. So death passed upon all men.
Romans 5:12b
"... for that all have sinned:"
Let's define the word death. We like to use definitions as we come up through Scripture. First and foremost, let's look at physical death because that's what we are most acquainted with. We see it on every hand. Not only in the human race but also in the animal kingdom, the birds and so forth. But, so far as the human race is concerned, death as we understand it. What is death? I think the simplest way we can put it is that death is separation. Death = separation. In the physical then, it is a separation of the body from the soul and spirit. Death is that separation of that invisible part of us from the body.
As we contemplate this whole makeup of man and his relationship to the physical existence; his relationship to God, it is good to understand some of these things. Whenever the soul and spirit takes flight from this body, we have death.