I recommend reading "Advice to the Stutterer." The Stuttering Foundation actually has the full book in PDF form for free! It will be useful for him specifically as he gets older, but it'll also give you an idea on how he might feel and techniques he should try again, as he gets older. [Advice to the Stutterer](https://www.stutteringhelp.org/Portals/English/book0009_may2010.pdf)