Great looking family there sir. Personally, I would get him a small 50cc quad or similar. Go over some safety rules with him backwards and forwards. Start off slow and let him follow you around or vice versa. I ride my grandson on the back of mine and he'll be 7 in July. He was thrilled beyond anything to go shopping for his first helmet and gloves. I don't think there is any "right age". I think you'll know when he is ready as far as aptitude and ability to take on a two wheeler all by himself.