I’d imagine you accept what is realistically available to you. You’d not really have anything in common with people outside a certain window so as you age these “older” people are just your peers from a similar vintage so to speak so a lot of things make sense and are common between you and each year they just happen to be a year older…
I'm pretty sure for me it's just that generational age differences squick me out, so when I was young, guys old enough to be my dad? EEW! But now it's also guys young enough to be my kids, EEW!
I do also agree about the maturity level, but that's not enough different between adults, a 35 year old can be about the same mental maturity as a 60 year old, I can talk so easily to my grown kids and their boyfriend/girlfriends/spouses, they are adults. But I literally don't see people that age as sexy.