I agree with about 90% of this, but I ought to point out that according to the movie, it's pretty damn likely that Steve was a virgin when he went into the ice (...or, at least a virgin with girls.) He outright tells Peggy he was never with a woman before the serum, and most of the rest of their courtship is about waiting for each other (although there's a fair amount of evidence that Peggy was more experienced...)

So while I will totally buy fics where he is making time with all the showgirls or Bucky takes him to his favorite brothels or whatever, the 'virgin!Steve uncomfortable around sex' fanon isn't because he's from the 1940s, it's because he's Steve. (The homophobe stuff is a little harder for me to buy, considering there's a scene where he thought Howard was propositioning him and all he did was act embarrassed and keep treating Howard exactly the same... although he would have very different conceptions of all the cultural things around what homosexuality means.)