I can't remember the first time that I started masturbating, but I think I had my first orgasm at 10. I was an only child and somewhat naive, and I didn't have any siblings to help me out. I remember getting erections at a young age, but I didn't connect that with anything sexual. I started noticing that when I saw a cute girl at school or even thought of one that sometimes my penis would get hard, but I still didn't think to stroke it or make anything else out of it.
Anyway, I went to bed one night around fourth grade and had been thinking of girls and sex, so I had an erection. Usually, it went away after a few minutes, but this one was persistent. I was quite hard, and even though I tried to ignore it, it just stayed hard. I was wearing loose-fitting PJs, so there was enough room for my penis to stay hard, and the light cloth rubbing against it just made things worse. I tossed and turned and tried sleeping on my stomach, which was uncomfortable since my I had to bend my erection down a bit even though it was pretty short at that age. Anyway, I finally decided 'the heck with it' and pulled down my shorts and started playing with myself. I really didn't know what I was doing and I just explored my penis and found that if I rubbed it under the head and the bottom side that it felt pretty good. After a while, it felt pretty numb, but a good numb. I kept on rubbing it, and suddenly my groin area tensed up and my penis suddenly started to spasm rhythmically for about 10 seconds. I was sort of scared because I didn't know what was going on. My heart was pounding, and I was shaking, but it felt pretty good. Eventually, my penis softened up again and I felt drowsy and fell asleep.
Oddly, I don't remember masturbating anymore to an orgasm after that until about 12 or so. Around that time, my parents gave me a book about puberty, sex, and all of that juicy stuff which I read enthusiastically. I really liked the parts about girls and how guys shoot sperm when they have sex or masturbate. I realized that that was what I was doing and that I had an orgasm back when I was stroking myself at 10. I decided to try it again that night. At that age, I was almost perpetually hard (well, not really, but it seemed that way) and always thinking about girls. So, one night I pulled my shorts down and started slapping and stroking the underside of my penis. I got that numb feeling again after a while, and backed off several times before going all the way. I actually stopped just a few seconds short of an orgasm and had sort of a 'fake' one, if that makes any sense, where only one or two weak spasms occur. After I calmed down, I turned the light on and noticed a drop of white fluid at the tip of my penis, and realized that I had ejaculated, which made me feel pretty good (I'm a 'big' boy now!). I walked into the bathroom and cleaned myself off and went to bed.
The next evening, I tried again and kept stroking through my orgasm, which led to a more powerful one with longer and stronger spasms. After turning the light on to clean myself up, I noticed that I had a whole stream of cum dribbling down my penis. Since then, I masturbated almost religiously every time after crawling into bed. I'd always turn on my side and shoot out onto the floor and clean my cockhead up on the side of the bed, which would usually leave a faint stain after a while (I hoped that my parents didn't notice and I'm pretty sure they didn't).
Anyway, I still masturbate virtually every day, although I use a different technique than when I was a kid. I love to look at porn on the Internet (especially movies showing women masturbating and cumming - I'm a big clit fan and love seeing a clit becoming erect) and masturbate at the same time. In fact, I think I'll go do that now.