I am now 19 but this must happened about four years ago since I remember I was 15 at the time and my brother would have been 13.
By the time I was 15 I had never had a boyfriend nor even been kissed, so you can imagine that I was full of curiosity about boys (not to mention horny as hell!). I used to look at porn on the computer and masturbate to it, so it wasn't as if I didn't know what a penis looked like, I did. But I was eager for more. Around this time my brother had a friend Adam, who was really cute. He was the same age as my brother but seemed older and always spoke to me as if he were the same age.
Anyway, one night my brother and Adam were playing in his bedroom down the hall, our parents were out. I had been looking at some porn and was feeling very horny and was about to masturbate, but the boys were making a lot of noise and it was spoiling things for me, instead of thinking about what I'd just seen on the computer I kept thinking about the fact that there were some real cocks down the hall. Why I did what comes next, I really don't know. Even though I've thought about it a lot (and cum to it a lot), I still have a hard time explaining it.
I went into my brother's bedroom where the two of them were playing some computer game. I started talking to Adam and eventually he stopped playing and made conversation with me, I could see my brother was pissed off with me for spoiling their game. I then went into some total lie about how our biology teacher at school had talked to us about masturbation and about how boys did it every day. By this time I knew my cheeks were red and my heart was pounding but I kept on. 'Do you do it every day?' I asked Adam. I tried to act as natural as I could when I said it, but I didn't feel that way. He said something, I didn't hear what, and then I was like our teacher said that some boys even do it three times a day. I said I thought that was impossible. Did he ever do it that much? My brother hadn't said a word, he must have thought I had gone crazy. Adam sort of giggled and I knew he was embarrassed. By this time my heart was pounding so hard but I thought I had to go through with it.
I sat on the bed and just summoned up the courage to ask Adam if he'd like me to do it for him. He didn't say anything, he just stood there in front of me. I'm pretty sure my hand was trembling as I reached out, got hold of the top of his jeans, and pulled him toward me. Without waiting, I unzipped him, pulled his jeans down a little, tugged his underpants down, and finally got to see in the flesh what I'd been thinking about for years. His cock was still soft and didn't look at all big at that point. I picked it up between my fingers, pulled his foreskin back, and just massaged it a little. I didn't dare look up. It very quickly got erect and I was surprised how big it was for his age. Not just long, but quite thick as well. Just like I'd seen on the computer, I started to jerk him off while he stood in front of me. Neither Adam, nor my brother, nor I said anything. It took longer than I expected, about three or four minutes, but eventually I felt his cock begin to twitch and then a huge load of cum spurted out from his knob over my top and carried on spurting four or five times. It was all over my fingers and I had to stop an urge to lick it off and see how it tasted. He put his cock away and stepped away from me. I didn't know what to say, I wanted to leave and go back to my room. But at that point my brother, who had been standing by the computer (no doubt watching in amazement) walked up and stood in front of me. Wearing only a pair of shorts it wasn't difficult to see his erection beneath them. Knowing what he wanted me to do (poor thing must have been so horny!), I pulled them down along with his underpants. His cock, obviously, was already hard and erect and was much more the size of what I imagined cocks of that age should be, shorter and thinner. I guess not surprisingly, he came after five or six strokes, shooting out everywhere and with more cum than Adam!
I got back to my bedroom as fast as I could and used the cum on my hands to give myself one of the best orgasms I've ever had.