I was about 13 years old when we moved to the city from a very rural area. In the country I could and would jerk-off outdoors every day. Once we moved to the city my play time was either in the shower every morning or in my room at night after my brother was asleep.
My brother is six years younger than I am and was always a pain in the ass. Most of the time I resented his existence and especially at night when I wanted nothing more than for him to be quiet and fall asleep. I would answer his stupid questions and pretend to be nice. I would then tell him I was tired so I would turn off the light and lay there quietly pretending to fall asleep.
I would lie on my side and listen very carefully for his breathing to slow to indicate that he was sleeping. While waiting I would pull my cock out the leg hole of my white briefs and slowly fondle with the helmet. (Many times I would fall asleep with my cock like this only to wake in the middle of the night and play without any fears.)
I would work myself to get rock hard while waiting. I would hardly move anything but my fingers. I would spread any pre-cum all over the helmet. Many times I would get real close to cumming but would stop because I wouldn't chance being caught.
When enough time had passed and I was certain I was safe, I could begin my masturbation session. Usually I would pull my dick out of the top of my underwear. I would rub the head against my blanket. It made the helmet feel so hot and intense that I could feel heat on the back of my legs. I would hold my cock at the base and swing the head back and forth against the cloth.
At that age anything could turn me on. Just thinking about jerking off could get me hard.
Thinking about different ways to masturbate also would create wood. I would get hard looking at a milk jug if I thought I could stick my dick in the throat of it, and I did try. While jerking off I could think of nearly anything to get off.
My favorite fantasy I used while jerking off was thinking of the hottest girls in school and watching them masturbate. One fantasy had all of kids on my bus masturbating at the same time, on the bus.
When I was ready to cum I would put my dick back in my underwear and I would cum into the cloth. Being young and full of cum, I would soak semen right through. I would lie silent, listening for any indications that my brother may have woken. I would then fall asleep with a happy penis. In the morning I would peel the head of my dick from my underwear and that alone would turn me on enough so that I would jerk off in the shower before school.