Hmm.. Good question.(For once)
It depends what you mean by strong. You probably mean strength and stuff. He's 16 and appearantly he started working out and stuff. He's probably not the strongest guy to break a brick with his bare hands but he's probably got his line of strength.
When it comes to willpower, I surely can't say for sure. He's probably not so easy to crack when it comes to like an mental invasion when someone would try to mindscrew him but you never know.