First off, I was 16 at the time and had a cousin who was 13. This particular summer we started hanging out a lot playing video games and stuff.
One day, we went swimming in my pool then he decided to stay the night. My parents weren't home but it was fine that he stayed. We continued playing video games and we started talking about girls.
My cousin, Jake, is pretty normal but well fit, and I'm the same for my age. We were sitting on my bed playing video games and talking about girls who look hot when I glanced over and I see that he has a huge boner (he was wearing basketball shorts so it was easy to tell) and he was repositioning himself. I took a bold move and asked him if he jacks off, but he said no though he has heard of it and wanted to know what it was.
I decided that I should teach him, and I also wanted to see his dick. By this time I had a huge boner myself and told him to take his pants off. He hesitantly did so and out popped his huge (I'm guessing 6 inch) uncut cock. I was very surprised as mine is only five inches and uncut. He has a small amount of pubes around his dick, making me even more horny.
I told him to watch me and I started jacking off slowly. He did the same to himself. I could cum right here but held off. I asked him if I could feel his and he said yes. His dick was so hard and felt great (I'm not gay though) and started slowly jacking him off. He did the same to me. I started going faster on him and he started breathing heavier and moaning. He said he had to pee, but I told him that he doesn't and it will be better than peeing. He let out a huge load with about five ropes of cum going onto my hand, his chest, and the bed. It was great. I told him to finish me off and he went even faster and started massaging my balls. I had one of the best orgasms of my life with a huge load onto him and me.
This night was great and was followed by many more.