If he shoots a 20 gauge slug he can handle the 7mm-08 easy. My buddies son is 11 and shoots every gun we have except a couple and he is not very big. His personal gun is a .308 though he shoots a 7mm mag quite abit as well. As long as you don't start them out on a large caliber right away they handle it pretty well usually. He has been shooting since he was around 5 though.