As the father of a giant, no chance that kid in OP is 6. Mine has always played up and still been the biggest kid, but he learns nothing dominating little dudes. He played up in basketball and still had 3" on the next tallest kid on the team and easily the tallest in their age bracket. He spent most of the season as 2nd string because he wasn't as experienced or solidly built as the 1st string kid.
Where it is all going to catch up and benefit him is when he is in 8th grade and everyone he has been on par with drops out of rec/select to play freshman sports. Then he is going to flat out dominate at everything, I haven't decided what he will do that year. He should have a spot at varsity basketball as long as he keeps growing and getting better.