My best friend and I had been friends for years before we ever really discusssed masturbation, we both knew the other did it, but neither of us felt comfortable talking about it. We had a lot of sleep-overs at his house, and since his computer was down there, it made for some interesting browsing. One night when we were about fifteen, we came upon a site not unlike this one, and found a story about two friends our age who had masturbated each other. He asked me if I had ever been interested in trying mutual masturbation, but at that point I wasn't, so he let the topic go.
A few months later he had acquired a porno tape that a friend of ours gave him. We decided that since there was no way we could get through watching a porno without jerking off, that we would masturbate inside our sleeping bags. After a few minutes of jerking off inside the sleeping bag, I was getting hot and sweaty, so I asked him if it would be okay if I just jerked off in the open. He admitted that he was getting really hot in his sleeping bag too, so we agreed to open them up at the same time.
Once we had, I noticed that his dick was bigger round than mine, but that my six-inch length beat his by about an inch. I wanted to see how much, so I asked if I could measure his with my fingers to compare. He wanted to do the same, just to make sure I wasn't 'cheating.' After feeling the unusual warmth of his fingertips on my dick, I asked him if he was still interested in mutual masturbation. His answer was to grab onto my now-throbbing penis. We adjusted our positions so that we could both reach each other's dick, and since I'm left-handed and he right, it worked out quite well.
With the new stimulation, it didn't take long for either of us to come. After we cleaned up, we had some more fun comparing size and shape, and jerking off together became a regular part of our sleep-overs.