Hey mate. I live in Australia. I'm 35 had a stutter my whole life. My personal advice is get him to see a professional speech pathologist. The best chance of overcoming it is early professional intervention. But don't try to correct him at home. Help him and encourage him with any speech exercises the SLP give him. But don't give him offhand advice. He doesn't need to stop and think or slow down, it doesn't work that way. Anything like that will just make him self conscious and possible stutter more. Especially if he's still stuttering at school age. Make home a safe place where he doesn't have to feel self conscious about his stutter. He just can just relax and be who he is.