Taekwondo/Hapkido is a very good martial art. I started training when I was 12 and it really taught me allot. Keep him in it for as long as he wants to learn and you will be contributing a great deal to your sons success in the future. It teaches respect, agility, fighting skills, confidence and self worth. You really can't go wrong with it. I would however stress that it won't make him a hardened badass. If he is dedicated to being that kind of fighter he will need to take it to another level where multiple styles and contact fighting are the norm. I would stick with TK for at least 8 years though.    Trust me.