All of my siblings(1 brother and 1 sister) started to stutter ever since we were in elementary school. We did not stutter so severely but it was bad enough that our parents were worried about our future. Interestingly, they had never talked about "it" until most of us were in college (17-19 years old). Only then they openly spoke about our stuttering, giving the advice to seek help from a psychologist, etc. Why did they never talk about it before? well, I asked them and their answer was that they just simply believe that, the more we were aware of our stuttering, the worse it would get. So what did they do instead to help us? They encouraged us to SPEAK UP. Sometimes, my parents would call me to their room and asked me to read some Bible verses and sing a church song. I hated it so much because I would stutter. but they said, "Do it for God!", and we were like "uh okay okay" lol. They had been doing things like this to us for years and none of us realized it was all intentional. Now, I can only thank them for doing that. So my point being is to avoid an explicit conversation about his problem until he gets more mature and instead for the time being to just encourage him to talk and speak up more regardless of his stuttering. Show it to him that it doesn't matter if he stutters on every word, but you are there to listen to him. Temporarily ignoring the problem seems counter-intuitive, but it actually makes sense given a lot of cases where parents hastily brought their young stuttering children to see some practitioners ended up failing. I wish your brother good luck, and he's lucky that he has a supportive sibling like you! :)