Reading the linked story by a 15 year old boy seeing another boy's hard, and jacking off together, reminded me of a similar experience when I was his age.
We were sitting in class, bored as usual, when my friend, Paul, sitting opposite me, glanced down to his crotch and made his obviously hard dick jump. He was watching me closely, and saw me smile at what he had done. I got an immediate hard-on, and did the same thing while he watched. When we left school for the day, he asked me to go home with him. I agreed, and when we arrived, no one was there except us.
Paul and I had never before discussed sex or masturbation, but he got right to the point by asking how many times a day I jacked-off. I told him the truth; two or three times. While we were talking, Paul was getting his clothes off,and I saw his big, thick, hard dick for the first time. He asked if I were going to just look, so I too stripped, and we began jacking standing up watching each other. It didn't take long for us to have orgasms.
After a quick clean up, he sat down in a chair and I on his bed facing him while we recounted our sexual histories. He left for a minute, and returned with the biggest jar of Vaseline I had ever seen, lubed up his dick, handed me the Vaseline, and we had our second mutual. After this first time, we usually got together two or three times a week for mutual jack-offs.