S.H.
My daughter is 7... and takes Karate. She LOVES it.
At her school, the starting age they allow is 5.
It is very good for discipline and physicality and learning appropriateness, self-control, etc. and is very beneficial in many ways.
But you have to choose a good school. Research it.
It is not about how 'strong' a person is or about 'winning'... it is about attitude as well. And if the Teacher(s) are good, they instill values in the children... the class, and about behavior and 'respect.'
It is good.... in that is teaches a child not about "fighting" but about control too... and discipline. About their body/strength/ability, and not using it in wrong ways. NOR is it allowed in school.... to cause trouble.
It might benefit him... as it does many kids.
For my girl, she asked for lessons. She wanted to take lessons. She loves it very much.
**Oh, I might add that one of my daughter's classmates, is a boy... a very big boy and very active, for his age... and thus, his Mom enrolled him in Karate so that he learns coordination/how to control his body/physicality etc. The boy enjoys it very much.
all the best,
Susan