I don’t know. I do think there is a fundamental difference in language processing in the brains of stutterers vs. “non-stutterers” (quotes because no one is 100% fluent). Personally I started when I was 4ish and my family moved. I went from fluent (old home movies attest to this) to severe blocking with secondary physical tics like throwing my head back and forcing out words within a few months. Ever heard of a valsalva maneuver? Essentially it’s the core muscles engaged in forcing things out of the body—either up or down. This has something fundamental to do with stuttering I think. At least early childhood stuttering. Getting out of your head is a big part of my fluency and general mental health strategy.