I was barely 12 years old when I concluded that God does not exist, during my first year at grammar school.
I don't recall thinking much about God before then, but when I started boarding at Skipton Grammar School they made me go to Church every Sunday. And most Sundays there was a good long sermon to which I could either listen attentively, or maybe find something more interesting to think about. I doubt that I did listen very attentively, but I certainly did devote some of the time to trying to make sense of this God thing.
I did find that pretty hard. But I worked at it for a while. The only reason why I worked at it as long as I did was because of all the very important, distinguished, able people who professed belief in God. It seemed inconceivable that so many of these people could believe in God if he did not exist. However, this alone could not suffice.
At the beginning of the second year it was customary, but not obligatory, to take classes in preparation for confirmation in the spring. By the time I had to chose, it was all over, for me the idea of God had no credibility, and I declined to attend the classes.
I had concluded that enormous numbers of distinguished testimonials is no certain guarantor of truth.
Though confirmation was optional, belief, or at least observing the forms, was not. In fact a disbeliever was obliged to suffer greater hardship in his worship than the confirmed believers, who were free to discharge their obligations by attendance at early morning communion. This service was not only shorter than the interminable matins, but, by being earlier, left the main part of Sunday morning free for more enjoyable pursuits.
Since I was obliged to give false testimonial every Sunday, at some inconvenience, it seemed more sensible all round to adopt a more advantageous lie. It did take me a few years to get round to it, but in the fourth year I enrolled for the classes and became confirmed, in order to qualify for early morning communion, a heavenly alternative to the hell of matins.
Anglicans are of a tolerant disposition. Though one must have been confirmed to take communion, disbelief is sometimes treated as a minor eccentricity. I have also on occasion been invited to act as a Godfather, for which role faith seems inessential.
When I still thought seriously about the possibility that God existed I was looking in a very general way for some concept of God that was coherent, consistent with what I already believed I knew, and relevant to my life. I wasn't particularly concerned with how closely it fitted with what the Anglican Church claimed about God. Still I couldn't find anything.
Also note, that I am not against belief without much evidence. I'm prepared to believe in something "on faith". And I do. Just not "God".