Sounds similar to me, speech therapy helped but wasnt a cure, I was a little younger (like 4), my parents said it pretty much appeared out of nowhere, am 28 now and pretty fluent although not completely, it got less severe until my preteens where it got really severe until I was like 15/16 and it got better. I don't particularly remember anything psychologically that happened to cause it and my parents acknowledged it pretty much immediately. No developmental issues (I don't think that's a cause tbh, I've heard anecdotally that stutterers tend to be of above average intelligence but I haven't looked at the data). Parents took it very seriously because they saw it had a terrible effect on me, took me to all sorts of doctors, specialists etc (I'm in the UK so fortunately that was all free, not sure where you're at). Ultimately I think it was a net positive, gave me tools that I still use sometimes to help with fluency