This happened when I was 14
I was staying with my friend for the weekend. We were close friends but it was an unspoken rule that we never wanked in front of each other. We both knew that the other wanked. We talked about girls and even porn but never got around to wanking with each other. If I felt the urge (which I almost always did) I would go down to the bathroom and wank in there.
It was about eight o' clock on the Saturday night and I had a piece of wood in my boxers. So I went down to the bathroom, usually I would knock first but this time I forgot. I walked into the bathroom and straight into my friend's older brother, Aiden, jacking himself off in the bath. I was so embarrassed, I didn't really know what to do. I was trying to apologise when he told me to come in, close the door and lock it. So I didn't really know what to do, but I chose to listen to him.
I couldn't help staring at his 16 year old cock. He was cut and he was just over 18 cm long. He hadn't shaved his pubes and he had quite a bush. I could feel my 15 cm dick growing in my boxers, he obviously saw it to. He told me that it wasn't fair that I had seen his dick and he hadn't seen mine. So I dropped my boxers and revealed my boner. I also still had my pubes. He had a snakes trail running up to his bellybutton, which hadn't started on me yet.
Anyway, he stood up and got out the bath. I didn't know what I was meant to do. He asked me if I knew what wanking was and I told him that of course I did. So then he asked me if I had ever been wanked by someone else before. I said no. He asked if I wanted to see what it was like. I knew immediately that I wanted to try it, but I pretended to think about it first, before saying yes.
He walked around me and put his dick between my butt cheeks (it felt so good that I couldn't pull away) then he reached around me and started wanking me. I tried not to groan but it felt so good. As he thrust, his dick slid up and down my butt crack. I came within three minutes! Then it was my turn, he sat on the toilet while I jacked him off (using both my hands). He took about five minutes to cum. But he blasted five thick ropes onto the bathroom floor.
Since then, we have had three more experiences together. But I'll leave those for another time!