Try to get him seen for anxiety. While he could definitely just be developing a stutter, the stress of starting school can put a lot of anxiety on you. There’s the idea of new friends, new classmates, new teachers, the possibility of bullying, harassment, drugs, etc and etc. It’s a lot for a kid especially at 5. Their brains are still extremely sensitive to this kind of stuff. And if he’s an empath, it’s a lot harder because you’re constantly soaking up everyone else’s emotions and energy so it’s very easy to get distracted from your own emotions and energy. While it’s not really necessary for him to be seen for anxiety because of this stutter, it’s still good to rule out if it is from anxiety or simply his brain being wired differently.