self injuring is very triggering for me, so I don't talk about it much or come here to this forum often-- I'm sorry.

(nothing against anyone that does-- I think it's great if coming here and/or talking about it helps you)
However, I feel OK to answer your question-- I first self-injured when I was 13 so I guess I meet the present day statistics-- though I don't put much stock in any statistics.
My mom told me what an idiot I was when she saw my arm and leg(at age 13)..... I've chosen throughout my life..... not to talk about it.
To all of you that self-injure---
mandy