I was originally raised in catholicism, but at the age of 10-12, I just realised that it meant nothing for me, that it was even a pain to go to the church. However, I don't believe it totally explain my lack of belief in Christianism but it may be one factor.
Started to grow within me some convictions, results of my constant contemplation and introspection. I don't like to see humanity as exceptionnal enough to deserve a God; I always thought we didn't need a God, that there was no reason that it existed other than a symbolic way of expressing the beauty and perfection of nature (pantheism?). When you teach that concept to kids, they learn it as if it was a person that had the control on their life, someone behind the universe - it's more conceivable this way - and over the generation, many think about God that way. I personally always thought that this God was all that surrounded me, my mere presence and this feeling that I was someone and could control my life, have decisions... "It is how it is"; I wouldn't describe it better. No matter if there's an entity behind it, it just doesn't matter. The only difference it makes is the people who believes in God and that put themselves restrictions or rules, or just a life guideline because of it. But if there was a God, he wouldn't care whether you believed in him or not; he is the perfection and so you are, as the whole world.
I don't even know if I believe in reality; I really hate to believe in something, because I don't and often you need to take position - like I just did - and show that you are right about stuff. I don't think anyone can know the truth; I'm a skeptical person which kinda explains my paradoxal vision of the world.