Paul refers to Jesus as the second Adam. Whether Paul believed in a literal first Adam, I cannot say. I can say that I do not believe in a literal Adam, and yet I think Paul was speaking to spiritual reality.
The basic Jewish perception was that God can have a special relationship with a people, a relationship that stretches over time. In their understanding, the people, of course, were the Jews, those who supposedly shared a common historical ancestry in Abraham. And the relationship was one of mutual agreement, what the Jews called a covenant.
The problem is that ‘nations’ are a legal fiction, and so cannot enter into relationships or agreements. Only actual, breathing individuals can do that. And so the pressure of their need to believe in such a relationship required the thought of representative figures. God makes agreements with actual men, but since those men are representative figures, the relationship actually exists between God and those the various men represent. Thus the Davidic covenant, the Mosaic covenant, the Abrahamic covenant. The Jews required the thought of representative figures to realize their intuition of a relationship between God and a community, over time.
This concept of representative figures enabled the Christian thought of Original Sin. Had there been someone who was representative of all of humankind, then the sin of that individual would be morally binding on everyone, just as the Mosaic covenant had legally bound all Jews.
The story of Genesis provided just such an individual, and the intellectual framework of early Christianity incorporated that opportunity.
Because I do not believe in a literal Adam, I do not believe in Original Sin as it is normally portrayed. But I do believe the creation of God’s children out of material stuff posed a difficulty that could only be overcome by a spiritual process that, in human terms, we can, because we have no better way of conceptualizing it, describe as requiring a representative figure. In this necessarily inadequate human way of speaking and thinking, the glorification of Jesus was the enduement on Him of the status of representative figure for all of God’s children.
Or as Paul, given his world, could imagine it: a second Adam.