No way man... you think 20 year old girls have got it together? Get outta here.
I've seen 30 year old "girls", my uncles ex is like a mid 40's little girl.
Pathetic doesn't discriminate by age, I tell you.
And yes, same goes for men.
But generally you will stop seeing flakes around 30 years old... you will see more consistencies. People that are still in their 20s are clinging onto their youth.
(ok, maybe I am biased by my own experiences and being a little too cynical)