I'd say that I first began thinking in a Satanic way at an early age. As a child, I had to attend a funeral, someone I didn't know, just an acquaintance og my mom's and grandmom's, I guess. After the funeral service, I asked my mom the question, "why do people have to die," certainly a normal question for all kids to ask at some point. My mother's answer was, "because it's God's will." Well, right away I knew something was wrong with that answer, and I wasn't comfortable with it.
Later, at the age of twenty, when I first read The Satanic Bible, to be honest I was terrified, because I still associated Satanism with Christian "devil worship." I read but I did not understand, simply becuase I did not have enough experience of life to understand and put the concepts of Satanism into practice. But the seed had been planted, and later in life, after I'd travelled a bit in the world and seen for myself how shitty, ignorant and hypocritical most people are, I was able to see my experiences reflected in the philosophy of Satanism. I cloistered myself away for some time, reading all books written by LaVey and Blance Barton, and finally I understood.
Some time after that I applied for membership in the CoS, and now Satanism is a part of my life, something I think about and feel on a daily basis. I now understand why I've always been something of a "lone wolf," why I heed the call of the dark. I was born for it, and it is so very true that Satanists are born, not made. Like Magus Gilmore has said, one can't read the writings and then say "I want to be that." One can't "convert" to Satanism. We are born for the night, so revel in it!