I'm a 17 year old stutterer and I'm gonna try to give you some tips - the worst thing you can do to him as a parent is to expect fluency. Stuttering isn't a disorder by any means but it certainly isn't something that can be avoided, by accepting it, and accepting that he'll have periods of intense stuttering as well as near fluency will bring you one step closer to having a better relationship with him. Try and put him into speech therapy but don't force his hand if he is uncomfortable. Look I'm only 17 so I haven't experienced that much yet - but these are things that I wish my parents did.