I would say that you certainly don't wanna find him and beat him up. At least not without verifying who it is you're talking to. The reason being... what if you show up and he really DOES turn out to be a minor? You can get into BIIIIIG trouble for assaulting a minor. Doesn't matter who's wrong or right, the law REALLY tends to frown upon that kinda stuff.
Of course... if he IS over 18... then it might be a different story LOL.
I'm a big believer in kharma. If this kid runs his suck frequently enough someone is going to shut it down. It doesn't have to be you. We have guys who study Tai jitsu (I think that's what it's called) at my school and while I haven't had extensive contact with them they seemed like reasonable, likeable people. I doubt that young twerp would fit in.
I believe my school was the address and site found by Slamurai. I dont have a student by the name used in the communication. He is probably using a fake name as a google search showed it was a character in American Ninja. Supply and demand problem! More horses asses than heads!