My cousin, who is 21, is going out w/ this guy. I belive he's definitely tooooo young for her, but she and the guy don't seem to think so. Even his parents and hers are cool about it, but I really feel uncomfortable when I go even somewhere simple w/ them because it just feels strange. So before I tell you this guy's age how much younger of a guy is 'ok' for a 21 y/o girl to date?