When my parents were still married, my mom sent us to vacation bible schools in the summer. She did so partly to get us out of the house (church daycare LOL) and partly because she thought that was what 'good parents's did so she would look good.
We also got dragged to various denominations- Catholic, protestant, and our grandma took us to her Morman church frequently.
By this time I was reading advanced books for a kid-reading at a 12th grade level as a 5th grader- and the "miracles" in the stories we got at VBS etc were no more fantastical than the sci-fi I was reading.
Fast forward to high school tenth grade at about 15 years old. A couple of us were hanging around the band room office at lunch as we often did and religion came up. I already knew I wasn't a christian- the belief system made no sense. But I said "I think there might be a 'higher power' out there but I don't accept the whole Jesus thing" to which one of my friends said "what are you ? Jewish"?
She said it mostly in jest but it got me thinking and I resolved that I couldn't square a deity with the universe. Especially not any of the deities that earthly religions push.
A few years later, at the behest of a girlfriend, I went to Catholic catechisms but it just didn't take.
Christians will say "what about the big bang and how can you get something from nothing?"
My response? They start from an improper premise that there was "nothing". They accept an ever-existing deity, but can't accept an ever-existing natural universe?
And there is some evidence that there wasn't one Big Bang to prove their "Let their be light" premise. The universe can be expanding and later contracting only to "bang" and begin expanding again.
There is no deity. Conditions for life on earth were coincidental and sparked by lightning.
My atheism was intellectual.
My wife's on the other hand was more emotionally started. When people ask her why she became an atheist she says "my mother died"
Indeed, her mother died when my wife was 18 years old. She got sick of the pablum condolences "She's in a better place now" type of blather!
Why isn't being here with her daughter the "better place?"
My wife has since bolstered her emotional atheism with more philosophical groundings from my perspective.