When I was younger, about 15, I was growing like any other teenager, and my hormones were definately kicking in. I had been masturbating for at least a year by now, and ejaculating the entire time. Any sight of a woman (or girl) would get me hard almost immediately, though my own hand was the only thing that had ever gotten me off.
One particular summer I found myself spending the week at my grandmother's house. We had a fairly large family (even though I was an only child), and I could find almost no time alone for the entire week. I was used to jacking off at least once a day, but sleeping arrangements made that impossible.
Towards the end of the week, the rest of the family decided to go somewhere, and I found myself alone in the house with my 13 year old cousin Katie. Katie was kind of cute for her age, but I never really noticed her in a sexual way. However on this particular day she was running around in a purple one piece swimsuit, and I found myself getting hard every time I was around her. It was hot, and all I had been wearing was black shorts, socks, and tennis shoes. I wasn't athletic in any way, but I looked alright.
Apparently, Katie had noticed my erection, because when I said I had to pee, she asked to come with me and watch. I looked at her kind of funny, and she explained that she had watched (and touched) her younger stepbrother, but she wanted to see what someone my age looked like. I had never been seen naked by someone else, but I kind of liked the idea, and being as horny as I was, I agreed. Katie walked into the bathroom behind me and watched as I pulled my shorts down, my 6 inch cock standing out at attention in front of me. Her eyes were locked on my cock as I tried to pee but couldn't (for obvious reasons). I told her I wasn't going to be able to pee while it was hard, and she asked if it would help if she held it in her hand. I knew that was just going to make things worse, but before I could get the words out of my mouth, she had her hand wrapped around me.
I just stood there and basically froze. I knew that if she didn't get her hand off of me, I was going to shoot, and I didn't want to gross her out. Katie looked up at me and said that when her stepbrother got like that, she would have to make the white stuff come out. Slowly she started stroking her fist up and down my aching cock, and in less that a minute I found myself shooting more cum into the toilet than I ever thought possible. My legs even got weak.
When she was done, she wiped her hands off and proceeded to stand there watching until I could finally pee, just like she wanted me to. I did get a treat by getting to watch her pee afterwards, too, but unfortunately I never did get to touch her.