When I was 15 my cousin aged 13 came to stay overnight. My Mother was out till early in the morning, so I was deemed old enough to look after him sensibly. We watched TV till about 11 or so, then I said we had better go up to bed. We did not have a spare bedroom, so he was sleeping on a camp bed in my room. Before we turned the light out I started reading a book I had found by the side of the road a couple of days previously. It was an adult novel with plenty of sex content and reading it was making me horny.
I always slept naked, so when I got up to get a drink of water my hard on stood out in front of me, as I passed his bed. When I returned he was standing up reading the book and I noticed his cock straining at the front of his PJs. My erection returned stronger than ever at this sight, but I didn't mention anything, although I enjoyed displaying it to him. He gave me the book back and I asked him if he liked reading about sex. He just grinned and got back into his bed.
I needed to jerk off, so turned out the light and got into bed. Feeling daring I pulled back the covers, hoping he would watch as I pulled away on my cock. Sure enough, curiosity got the better of him. I heard him get up and walk over to my bed. Still wanking myself I motioned for him to lie next to me, which he did and without a word took off his PJ bottoms. I could make out his stiff cock, which was nearly as big as mine, and just as stiff. He started copying my movements and soon we were both wanking with the same rhythm.
Again, without a word I moved my hand onto his cock and he did the same on mine. It didn't take long before his cum shot out over my fingers, which sent me over the edge and I shot a great load over his hand. He then went back to his bed and I licked his cum off my hand. I then had another noisy wank and I am sure he did the same, although neither of us spoke about the experience and we never had the opportunity to repeat it, sadly!