[female, age 17, first began to SI at age 15, college student]
Yes. I actually know a surprising amount. In high school all of my friends did it. Literally all. We all started doing it separately and found out over time about each other. After we all knew about each other it turned into a sick kind of competition to see who could cut the most or the deepest without any of us ever acknowledging it. I also know that my boyfriend used to self-harm. He has influenced me on how it is possible to get better.