Honestly I have no idea. I never stuttered as a kid or during the first half of my teens, however I think for me it could be something related to dopamine. Growing up, I had mild Tourette’s and would have uncontrollable tics like facial blinking, sniffing, etc. I ended up outgrowing this but it came back at age 18 worse than before along with my newly developed stutter. The human brain and body is just weird like that