I'm 29, so... I'd say it felt "over" by 25 honestly.
Then again, I feel as tho as soon as HS ends, it's pretty much over, unless you have some sort of back up plan and you've got friends that'll hook you up or something, but with the way things are looking nowadays, especially with how more and more people are becoming loners and shit (just because it's cool and trendy), I don't see anyway out really.. Besides, most "friends" backstab and ghost your ass as soon as the opportunity of a foid presents itself to them. You'll just be "old news" and no one wants to hang out or be associated with the guy who can't get laid. Life sucks and then you die.