I tied myself up w/ hand cuffs on ankles and wrist and swiveled clumpsy around on a carpeted floor. I suddenly got an orgasm and the carpet went wet. I had no idea that day what had happend to me and was very afraid somthing went wrong. I might have been eight years old or even younger, attending the primary school. The handcuffs I used those days were these for kids to play sherrif or police officer. You could buy them in any toys shops and looked almost like the darby style cuffs we use today. I have no idea what motivated me to do so but I suspect some of the Tarzan movies and 'Devil at four o'clock' might have had some influence on me, in which prisoners where chained together and arrested. I also whipped myself with a rope. Sometimes I slept w/ handcuffs on during the nights. There was no suspicious about it as my parents had no idea what the background of it may be, since I was too young. Later I learned that I had indeed an orgasm and sperm ejaculated. I practiced this for several years before I really got to know what an orgasm is... as a teen then.
So this was - in one way or another - the first time. But I would not call it D/s lifestyle. Please mind that there were no information about SM available those days. And sexual life styles were not discussed, neither in public nor behind the curtains. Mind this was in the late 60, early 70. Many years later my parents told me a bit about sex and I somehow got to know what masochism is.