I think when i was 9 or so.
It wasn't even forced, all i could remember from it was that i did it out of reaction, since my friend got bullied and picked on from the some higher grader. I mean, he cried right after school everyday and it's because they also harmed him physically... aswell as mentally.
Oh yeah, i think i got suspended from school for a week since the bully got injured and couldn't attend school because of that.
Your age when you first developed an interest into something