I started to masturbate when I was maybe 11 and quickly found fantasies to masturbate with, in Penthouse and a book called The Pearl.
I guess very early maybe 4 or 5 I didn't realize it but I found sexual pleasure in domination themes. I think this is built in somehow. So when I discovered the written word and pornographic stories I gravitated to those that had an S&M component.
Ditto with pornographic movies and videos although I never really got into these so much. I would use pornographic stories and read them and masturbate to these, often over an hour or two.