I’m almost 41 and have been a life long stutterer. He’s going to deal with it his entire life and the fact he’s doing okay with it now is amazing. I still run into adults that think it’s hilarious to mock me. I used to completely block and still can’t say my name properly or my birthday. As I’ve aged it’s gotten better though. There is nothing you can do to stop it. People are cruel. As someone who stammers and freezes, you just get used to it. It will get easier for him as time goes on. There are always going to be people that defend him, too. I’ve had strangers tell others to stfu before, haha It’s part of our lives, there is no cure. It’s like having a birth defect that people can only see when we speak. Just love and encourage him to stay strong and not allow others to bring him down. You’re doing a great job.