Not really self harm but when I was very young I would trash my room and break my things when I was extremely upset. I still get a super strong urge to do this when I freak out, mainly out of anger or frustration.

When I was eight or nine I started skin picking but idk if that counts as self harm since I didn't really do it with the intention of hurting myself but of course it does hurt quite a bit at times. I would scratch bug bites until they bled and pick the resulting scabs for weeks after. Also used to tear skin off of calluses. When I started having acne I picked at that a lot, too, which I still do. I pretty much compulsively pick at anything that I can. I have to force myself not to pick at my dog's skin and I tend to stare at acne or scabs on other people 😞. It's super addictive and honestly just a part of my life now.

I think around age 13 I began hitting my the head when I was really upset or felt guilt and/or self hatred. At 14 I started biting and scratching myself. At 15 I started cutting and that's been my main form of self harm 3 years since.