I was in middle school.
After months of looking at my dad's dirty magazines, I was wondering what sex would feel like. So one day when I was home alone I stripped, make a fist, ran warm water over my hand to simulate a lubricated vagina, lied down on the bed, and fucked my fist. My back arched several inches (in my memory it arched several feet--ha ha) as I climaxed.
After that, it was not so elaborate. I did count my orgasms for a while; #100 was the first one that was not dry.
When I started to feel attracted to other boys (two in particular) I tried to shut down those feelings. But they just grew stronger and more & more distracting. And I could not stop looking at them in class. Finally, one night I succumbed to the urge and thought about the two boys while I jerked off. It felt great and I then knew I was gay. And I could stop looking at them in class.