Paintballing is great, however, just have to worry 'bout kids cryin' when the first one hits him right in the chest.
I did for my 14th birthday. It was really fun. Rented out the whole place and bought several cases of paint.
I gave up on paintball and airsofting, though. Just wasn't real enough for me. So I swapped to trap making, shelter making, hiking, and killing things with my FBM. <img src="/ubbthreads/images/graemlins/laugh.gif" alt="" />
Sorry 'bout that, anyways, it's true, At around 13-15, maybe beyond, most boys really like paintball. It's definitely fun.
Honestly, if they haven't gone paintballing, at least take them once. Find a nice paintball center, rent it out for the day, buy a few cases of paint, play a bunch of games: Capture the flag, terminator, bunkers, etc., etc. They'll have a blast.