I would recommend you aggressively work on his stutter when he’s younger. Mine didn’t bother me when I was younger and I didn’t think about it much. Therefore, I didn’t work on improving it. Once I started working my life has been miserable. I can’t skip over words as much and I’m trying very hard to improve my fluency. I would have him read book passages and practice impromptu speaking with you. I can’t stress how important it is to focus on it when he’s young vs older. When you’re older it’s much much harder to overcome.