Reading the linked story reminded me of my first mutual jack off with a friend.
By the time I was twelve, I had been masturbating for about two or three years. I was introduced to it by an older boy, but except for that had never masturbated with a friend.
At the age of twelve I had a thin line of hair just above my penis, which by then was about five inches hard. One day after swimming class, my friend Jim remarked that I had developed a big peter for a 12-year-old. I found his remark flattering and exciting, but also frightening in that I realized that he might guess that I was jacking off. In return I smiled, and said that I was happy that he liked it, and thought no more about our conversation.
The next week, he invited me to spend the following weekend with him at his grandparents summer house. I accepted, and when the weekend came we went to the summer place. That night we shared a room with two beds and an adjoining bath. After bathing, we watched TV, and were completely ignored by the adults. Jim steered the conversation around to girls, and we both got hards. He noticed my bulge, and asked if he could see it. I blushed, but couldn't resist, so I slid my briefs off and my five incher popped out. Soon we were fondling each others penis, then jacking ourselves. He came over to my bed where I was lying face up, legs bent, pecker in hand. He asked if he could jack me. I agreed, he lay down next to me, and started jacking my penis with his thumb nearest my abdomen. Then I began jacking him the same way. Neither of us lasted long, and I had the greatest orgasm possible for a 12-year-old as I'm sure Jim did as well. From similar stories, I conclude this is a common rite of passage for boys.