It good that your son wants to start using the internet for more then just Facebook.
I would start him off with something simple and FREE, such as phpBB. Have yourself as the Master (Super) Administrator and him as an Admin. Censor a few things to prevent him from linking to well known file sharing sites & from anyone uploading files also.
From time to time... Pop in and keep an eye on him.
I think its better that he came to you, then rather doing it behind your back.