A person between the ages of 20-24, who acts or looks like a teenager. You can sometimes tell a post-teenager by what the wear or listen to. Most Post-teenage Guy's and Girl's usually listen to little Wayne, wear hollister shirts, and use the latest IPhones or smart phones. Mainly because that's what the think most Teenagers find cool.
Notable Post-teens: Zac Efron, Demi Lovato, Joe Jonas, Taylor Swift, Macaulay Culkin (before 25), That one guy from Glee, Frankie Munaz(before 25), and soon to be Justin Bieber.
Guy 1:Hey man how old are you?
Guy1:oh, so you're in your 20's? I'm 23
Guy2:No I'm a post-teenager, 20's sound so old fashion.