FRrom your description I can clearly understand why you think 20-21 year olds are larger. It's been so long that you simply forgot.
Now, to answer your question. No, I have not noticed. In fact I don't pay any attention to the size, I rate the way they use what they have over size and I'll confess the older are more experienced that the younger.
Yes indeed #1. And I have also learned that the older devote more to satisfying me while the younger are there for their own satisfaction. They shoot their wad and they are finished. The older seem to count my orgasms and hold off on their own until they can clearly tell that I have been totally satisfied.
#1 and #2 i agree with both of you boys of that age bore the life out of me i prefer a real man who knows how to please a woman and wont cum too soon, I've tried a twenty somthing guy once it was the worst fuck i'd ever had i was left frustrated and angry as he came way too soon then went off to play computer games, NEVER again now i stick to real men not silly boys who have no idea what a real woman needs, As for size it means little to me i prefer a man who knows what his penis is for rather than being egotistical about his size average size suits me fine with an educated ass behind it of course.