I was never what one might call a dedicated theist...I was raised Catholic by parents whom I never realized were quite as religious as they later turned out to be. Or maybe their faith just began to get more important in their lives as they got older. They are both over 80 now, and seem more and more involved in the church.
At any rate, I guess I had some vague sort of idea of god when I was young, but we were not Bible readers, so my knowledge of Bible stories was limited to those same verses which come up, year after year, on schedule, during the Catholic Mass, and the occasional Charlton Heston movie.
I was, however, a pretty voracious reader. In my early years I enjoyed a lot of fairy tales, and after the age of 8 or 9, various mythologies joined those. And, honestly, I don't think it ever occurred to me that the stories of the Bible were NOT fantasy. It wasn't until I happened upon my dad kneeling at the foot of his bed saying prayers. Until that time, I think I'd just assumed that it was part of a bedtime ritual like stories and lullabies, but somehow it had never occurred to me that it was something "grownups" still did; that they actually took it seriously. For whatever reason, that just put me off. I think I lost a little bit of respect for my dad at that moment.
Later on, I always found myself trying to wedge Christian beliefs and those of other religions into some sort of Universalist philosophy. Though I'd never so much as heard the word Universalist back then, it didn't make sense that one religion would be right and all the others wrong, and if there was a god, he must somehow accept all these paths as simply different ways to reach the same destination.
I suppose I was reasonably happy with that conclusion.
Then I met my first Fundie as a Junior in High School (they were still fairly rare in Connecticut back then. Even though we are still not exactly overrun with them to this day). And the notion that every single person who was not "born again" and didn't have that "personal relationship with Lord & Savior Jesus Christ" was irredeemably bound for hell just hit me as so fundamentally wrong; so completely evil (if, indeed there was a deity which worked that way) that it completely turned me off from anything to do with Christianity at that point. If that was the way god worked, I wanted no part of him. And, ultimately, it became clear, upon doing more and more reading of both sides of the argument, that the only way it all made sense was that most probably god did not exist.