Although I have never seen definitive figures, I'd be unsurprised to find that most atheists at least in the US are deconverts.

I was raised to be a fundamentalist evangelical Christian and decided to get out when I found that the beliefs I had, and expectations that had been set, and just my whole mental model of reality was horrible at explaining or predicting experienced outcomes. I simply got tired of being wrong all the time. Also I did not want to be angry or frustrated or hurt or disappointed or confused all the time. Life is too short to live like that.

I started drifting away around 1990 for as much practical as philosophical reasons, self-identified as atheist by 2000 and was fully "out" (other than professionally) by 2005. People who were Christians and knew me as a Christian tended to assume that I was just going through some sort of phase and I did nothing to disabuse them of that notion. People who were Christians and had not known me as a Christian tend not to believe I was never a Christian in the first place. Those I just laugh uproariously at.

I was 5 years old. Born and raised in the bible belt (ky). I questioned my mother on why people act like a book is the truth. This led into a conversation where I asked my mother "Well, green eggs and ham is a book. Does that mean it's true?".

At five years old I challenged my entire upbringing. Did I fake it throughout high school? Yes for the most part. At college is when I really took the plunge. People are more open to a logical argument vs. Blind faith.

I was never forced to church, forced to pray etc. But it was what you would deem a "christian household". Throughout my years of faking I have read the bible front to back on multiple occasions searching for inconsistencies (of which there are many).

Most of my family is gone now but basically in order to keep up appearances I can play along as though I'm just as religious as the next person. A few member of my family don't accept it so I always have to hear things like "just pray" so I fake it. It's less stress for me to not have to hear it all the time and it makes them feel more at ease. I can deal with lying. In the end it's all just a combination of words designed to elicit a response. I'm merely manipulating the reactions.

I think that most atheists/agnostics were probably raised in a Christian environment.

Yes I was. I proved there is no Christian god by logic and science. On many occasions.