I am 30 years old and I have had Trichotillomania since I was 8 years old. I still have the issue. It is such a sensitive issue that he may not admit to it or when he does he will be defensive. Sometimes it starts out as an itchy scalp or just a general habit for your hands to go somewhere. It soon turns into an obsession.
I will be happy to talk about it in more detail or about my experience if you would like. You can e-mail me at: ____@____.com
In the meantime, please don't berate him or make an overly big deal about it. You might ask him if he would like to get his hair shorter which would help him to not be able to grab his hair. Also, if you do see him pick his hair, offer something to do with his hands. He might be stressed right now. Ask him if he is associating anything with his pulling. For me initially it was fascinating to find the "crinkily hairs" or the imperfect ones.
This might be a good inital resource for you: http://home.intekom.com/jly2/