Hey, In my opinion there is no benefit in pin pointing the original cause of your stutter. Knowing what caused it won’t cure it, unfortunately. I don’t know your grandad and I don’t agree with his behavior towards 5 year old you, but I think he has good intentions towards you. I wish someone told me at a young age that it is embarrassing, and I should fix it, instead of ignoring it and suppressing it with video games and isolation. It hurts to hear but perhaps it is the truth. Leave the past as it was and better yourself today. The earlier you start improving your life (not only your stutter) the better your future will be. Of course, I did not experience what you did, and it is easier said than done. Good luck my friend!