Another speech language pathologist here. The advice above is good. Make you show that you care about what he says, not how he says it. Don’t tell him to “stop and think,” or “slow down.” Make sure he has plenty of time to share with you. Ignore the stuttering. It is possible that he is a “clutterer” rather than a “stutterer.” Your description of him thinking faster than he can speak sounds like it might be the case. If he is an active child, possibly with ADHD, he will be more prone to it. If he speaks rapidly it could be cluttering. It might be worth looking into.