It’s possible that you were dealing with certain factors that you weren’t aware of at the time. Or there was some small trauma that triggered your stuttering. It could’ve been a bad test grade that shocked you, a bully, or taking a ball off the face at recess. Or maybe a nightmare while you were sleeping. Or maybe you ate too much junk food and it made you feel down. You may be able to recall it if you think about what was going on in your life at that time. I think most peoples’ first time stuttering is usually triggered by something that brings their health down or causes them to go into fight or flight mode.