It wasn't a choice.
You want the story, here you go...
In my childhood, I grew up in a household of religious folk. My family was religious as were my neighbors and their kids. Starting in preschool, I went to a Lutheran school. Preschool through 6th grade. A private Lutheran school. Starting in 2nd grade we were required to memorize a bible verse every week. Every Wednesday was church day. We'd take an hour in the morning, file up and walk to the church on school grounds, sit there listening to the sermon, sing Jesus loves me this I know, and go back to class. Everyone believed in god. Except me. Even in 4th grade which would make me what? 9? 10? something like that... even then I knew something was wrong. I didn't belong at this school. I didn't believe the things that they believed, and I felt it deep in my core. Something was different, but I couldn't put my finger on it. I kept telling myself I believed in god, I'd go to church with my family on sunday, sing all the hymns and hers, pray at the dinner table... but it all felt awkward. It didn't feel right, and I didn't feel comfortable doing it. Until one day I found out that there are others out there that also don't believe in god, and they call themselves atheists. That's when I started to learn who these people are, and right away I felt more comfortable. Just knowing that I'm not alone in this feeling. It was only at that point that I started doing more research on it and figuring out the logic behind it.
So by your argument, at the age of 10, I made a conscious decision to defy everything everyone has ever taught me about god and decide that meh... that's just not for me. And never look back.