imho, boys wear them to show off.when they reach the maturity and think that it was all in vain, they'll quit it.I never had one, or a tatoo, or any kind of "cool" stuff.
At my company there's a distinct difference between the blue collar and white collar sides. On the blue collar side, guys of all ages have earrings. It's completely acceptable, as are tattoos. On the white collar side, a few young guys in their early 20's have earrings and some older guys have the marks, but don't wear earrings. (I do know a couple guys who wear earrings outside of work.) The white collar side of older, established companies tend to be conservative by nature. People get ahead by emulating the actions, dress, and manners of the management. As a result, I think people feel they have to conform, hence the earrings come out.