My very first orgasm: I was well under 10 and, while in the middle of playing with a hard plastic ball, I happened to roll it between my legs and WHAMMO. Talk about a shock! LOL.
The first time I started masturbating: I couldn't quite forget the time I just mentioned above. I was 11 and started by laying on my stomach and humping my hands/fists. Obviously I had NO clue that what I was doing was sexual... ahh the age of pure innocence... but man was I ever hooked.