I was born an atheist, just like every other child.
My very large and very Catholic family took it upon itself to change this situation, providing my life with priests, religious references and visits to churches aplenty. But apparently my case was particularly virulent, and the whole concept of the supernatural remained incredible in my eyes.
We lived in front of a church, and I remember myself at age 8 or 9, crossing the street and going in by myself, imagining how it would be to believe. People seemed to enjoy deep experiences, praying to wood-and-plaster saints and virgins, showing mystical expressions after confession, dreamy eyes and all. But I just couldn’t. It felt simplistic, fake and hard to swallow.
At 16, after a heated argument with my priest regarding the evidential problem of evil (a name I was not aware of at that point, of course) regarding atrocities against children in Biafra and Vietnam, I finally told my family their efforts had been fruitless: I did not believe in their god, nor any other. They never got over it.
To my fortune, around that time I found the writings of Bertrand Russell. A man vastly more intelligent and respectable than me had thought along the same lines, and more rigurously, and with academic flair and sound reasoning. It was comforting. He was my first atheist friend. Many came after that, fortunately not all (in fact, none other) in the guise of elderly British philosophers.
I then spent time and a few philosophy courses examining the evidence in favor of religion and theism. It was no longer a matter of “I can’t believe it”, but became a question of “what if there is really something there and I’m just being a stubborn ass?”. I looked at religions and spirituality in various guises, and had the mandatory 70′s dabblings in the paranormal. I then concluded my native atheism was not unfounded at all.
Then it got complicated, and I became a militant rationalist, but that’s another story.