My first experience involving masturbation
I was ten when I first saw a penis that had gone through puberty. It was my 14 year old cousin's, we were sleeping in a tent in his backyard and he opened up the front of the tent and urinated into the yard. While he was kneeling I had an unobstructed view of his penis and it looked just like mine but swollen. We were both circumcised and we were both caucasian so we had the same circumcision scar, about the same color and obviously the same head shape. His just looked like a fatter, swollen version of mine so I asked him 'why is your penis swollen?' My cousin seemed insulted he said 'it's not swollen' and I asked why it was so big. He told me that it got bigger and he got his penis out again and began flopping it around until it extended and became less... well, floppy.
He kept playing with it long after that and the entire time he had my attention and after a while he ejaculated and I had no idea what had happened I just saw this white liquid pumping out of his penis onto the floor of the tent. I was confused but my cousin told me that sometimes it happens if he plays with his 'dick' too much. I accepted his answer without too much further discussion even though I had many more questions, the only thing I really found out was that as soon as I got hair on my privates like he had I would have the same thing happen to me. I agreed to not ever mention what happened to anybody and we slept together in his tent quite a few more times and although we didn't play around again we were never shy about being casually nude in front of each other.