I didn't start any structured type of program till I was 11. What I can tell you is that boys like to wrestle and it doesn't matter what age. As long as there is structure, kids listen to authority and don't use anything they learn outside of training (which I know will be hard as boys will be boys), then I don't see it being a problem. As a parent as long as you leave it up to them if they want to continue with out any pressure then this is great. If their want to go starts to wain then do not force them to go; it doesn't work ... I know this from my daughter quitting TKD; I had to let her no matter how much I wanted her to continue training especially since she was very good at it; it came natural. Let kids be kids.
"IF I COME ... I'M BRINGING THE PAIN WITH ME"