I also started stuttering around your age (ages 11-13). It started off very mild, like barely noticeable but got significantly worse over the years. I am in my mid twenties and it feels like I have a moderate-severe stutter these days where I trip over words or get hard blocks/repetitions every 2-3 sentences. Like for me it got worse during highschool and significantly worse during university and it feels like its pretty much been the same since than.