I know it started for me when I was 12 and a series of traumatic events happened. I didn't have much of a stutter before, but after a mushroom trip I was able to remember about these things and put them together, then realize what caused it and how only with my father I still stammer the worst. There is some occasional stuttering that 2 family members have which is where I was but the trauma pushed it to where it to a severe degree. Still gets better and worse now.