When I was 13 my mother, brother, and sister went to visit grandma for a week. Since I was playing Little League baseball I stayed at home with Dad who worked during the day, leaving me home alone. I was beginning to feel stirings in my penis but had not yet discovered masturbation. That was soon to change.
In exploring the basement one day I discovered a stack of girlie magazine my Dad had hidden under his workbench. As I paged through them, looking at sexy women with big breasts and bare nipples my cock began to get very hard. Pubic hair wasn't shown in those days, just tight panties that showed a bulging pussy which made me even harder as I could only imagine what treasures were hidden by those panties. I took my pants off to let my cock free and as I looked at the pictures it throbbed and twitched. I didn't know anything about how to jack off but finally discovered that if I used my index finger to rub and tickle the area on the underside of my penis just below the glans, it felt very good.
As I was looking at a photo of a woman with big dark nipples and a large bulge in the crotch of her panties I kept rubbing the magic spot on my penis. All of a sudden I felt my cock began to spasm and tighten up, pointing almost straight up. It jerked and twitched, then the muscles just behind my scrotum began to spasm and even my asshole contracted. I was evidently having my first orgasm and it scared me. A few drops of clear fluid came out of my penis and I didn't know what had just happened. I thought maybe I had done damage to myself.
Curiosity got the better of me and then next day I again began the process of 'tickling my penis' while looking at the naked pictures. Sure enough, it did the same thing. Over the course of the summer I must have jacked off at least three or four times a day and began to squirt white stuff that looked like shampoo out of my cock.
Later in the summer I had an experience with both the neighbor lady and her grand daughter, not at the same time. But that is another story.