When I was 13 (eighth grade) my dick had grown large and got hard all the time. When that happened, it became pretty large. I didn't know about masturbation or sex. Just that my dick got awesomely big and hard from time to time.
Maybe I was an exhibitionist. Not only did it get erect in a seriously jumbo way, but I wanted certain guys to be impressed by it. Obviously I could not go around offering to show off my erection. But I came up with a plan. Whenever I could I would stand next to slightly younger boys (sixth or seventh graders) while urinating. That is, they would be in the restroom to urinate. I would be there to hope they would notice my big hard dick.
When I stood next to another guy at a urinal, my dick would slowly begin to rise up and get big. I kept my eyes on my own business, enjoying the process of becoming erect. The other guy almost always noticed what was happening. I could tell if he was looking at my dick. Sometimes a boy just stood at the urinal a moment too long. Occasionally one would clearly stare at my boner. And very rarely a boy would have a response that really excited me - he would get hard also while peeking at me.
Those rare occasions of another boy's dick swelling up and poking out gave me major thrills. The dicks were a lot smaller than mine, but seeing those stiffies made my day. My boner got harder and longer, if that was possible.
I never touched anybody, never tried to make contact or show any interest. I just showed off my big boner and drew incredible delight from another boy watching.
We became sort of buddies. There was never any physical contact, never a word spoken, but after his demonstration I also learned the fine art of jacking off. We watched for each other to go to the restroom. We would stand next to each other and pump ourselves without letting on that we knew what we were both doing.
Within minutes we would shoot our loads and hurry back to recess or lunch or whatever.
I was embarrassed at what we did. But now that I look back on it, those quick wanks between a seventh grader and an eighth grader were moments of sheer delight. We were curiously mismatched. He had a small, immature stiffie but was wise for his age. I had a large and mature one but was ignorant until watching him.