Was raised non-denominational Christian, and did believe until around 13 years old when upon my 5th re-reading of the Bible that I noticed there were two versions of The Ten Commandments and started questioning why a perfect god would need a second version, wouldn't a perfect being get it right the first time? It was more or less happenstance that I got this thought while reading. It didn't make me atheist there and then, but it got the ball rolling, so to speak. I think I realized I was atheist by the time I was 17 years old.
Also, during those 4 years I had a lot of self-doubt and fear of my eternal soul because I was still in the clutches of the faith, and the thought of an all-seeing peeping tom didn't make it any easier. After those 4 years when I realized I simply didn't believe any of it, it felt like such a burden was lifted off my shoulders, that I was truly free of the fear of hell, and the thought of an all-seeing peeping tom monitoring my thoughts and actions every moment not being there. There is no eternal soul, there's no hell, there's no heaven, when you're dead you're gone for good was quite a sobering realization.
Also, during those 4 years I had a lot of self-doubt and fear of my eternal soul because I was still in the clutches of the faith, and the thought of an all-seeing peeping tom didn't make it any easier. After those 4 years when I realized I simply didn't believe any of it, it felt like such a burden was lifted off my shoulders, that I was truly free of the fear of hell, and the thought of an all-seeing peeping tom monitoring my thoughts and actions every moment not being there. There is no eternal soul, there's no hell, there's no heaven, when you're dead you're gone for good was quite a sobering realization.