I started puberty just before I turned 12. When I was 11 my dad gave me a sex education book and told me to talk to him if I had any questions about it. That was the beginning and end of my sex education. I was (and still am) an avid reader, so I soon had read and re-read that book. By the age of about 121/2 I had a neat little bush of pubic hair and a penis that had grown a lot in a short time. It was also frequently getting erect at odd times. Although I had read about wet dreams and masturbation, I had not yet experienced them.
One rainy afternoon I was alone at home and lying on my bed reading. For a few weeks now, when I had an erection and privacy, I had been idly playing with my foreskin. What I used to do was grasp it with my fingertips and gently twist to and fro round my glans. It naturally felt good, but I wasn't consciously masturbating and I had still not ejaculated. On that rainy afternoon though, maybe I went on for longer than usual, or maybe my semen storage system had reached capacity, but suddenly I was overcome with that wonderful feeling that you have all had and things erupted in my underpants.
I went to the bathroom, cleaned up as best I could and put my underpants in the wash-basket. I am sure my Mom must have noticed the mess in them, but she never mentioned it. After that I used to bring myself off in the same way two or three times a week, until a friend showed me the usual pump-action grip.
Although I am married now I still masturbate several times a month, usually with my original twisting technique, and usually when I am reading.