I was around 16 at the time.
As a kid I had a really great buddy (Dave) who lived next door. We would spend a lot of time swimming and doing the fun stuff kids do.
Naturally, we were sexually curious and it wasn't long before we were hiding in his dad's tool shed jacking off together. Dave was 2 years younger than me so I always felt obliged to teach him what I had learned.
He was always ready to try anything I suggested and so I said that this time we should face each other really close with our dicks almost touching and go at it til we cum. We usually did it facing away and just stole the occasional peek at one anothers hardon.
He agreed and so there we were, on our knees with our stiff cocks bobbing head to head as we stroked away. We were both leaking a bit of precum and as our boners touched every now and then it would spread over our swollen heads. This got us both very excited and it wasn't long before Dave told me that he was going to cum. I told him to stay just where he was and shoot his juice over my throbbing meat.
With that he let out a grunt and a wad of warm, wet cum shot out of his cock and hit mine bang on the head followed by three or four more smaller streams.
It felt and looked (and smelled) absolutely amazing and it was a matter of seconds before I was in the throes of a massive orgasm. My cock pulsed and throbbed as white streams of jizm pumped out all over his still dripping boner. The first shot landed just under his belly button and caught in the top of his sparse pubic hair. As the last bit oozed out of me I touched his cock with mine and we just stayed in that position for about a minute letting that warm goo mix. We were both still stroking ourselves lightly, enjoying the slippery wetness of our cum, not saying much except for the occasional 'wow' or 'mmmm'.
It was a great time and we carried on jacking together on and off for another 2 years, but we never repeated cumming on each other's cocks. I still use the image of that session when I jerk off today and it never fades or loses it's appeal.
Dave's mom caught me jerking too but that is another story.