I've been learning Karate since 3 or 4 months now and thou that I'm still young in it, I have learned many things like discipline, helping others, self-esteem, self-respect, respecting others, participating in good things, encourage myself and others and so many things like that.
I think that learning martial arts is a great thing for anyone at the kid stage and for the adults too.
I practiced it for five years. Precisely, I started at the age of seven... I recommend it to any youngsters. At that age, there's a lot of energy, and they are still forming their values and discovering their potential. And martial arts can definitely show them great virtues.