I would have to say 30, while sitting in church. Took a long time to get there, although I was never a holy roller. Just a believer who enjoyed the people in my church and our activities. (joined that particular church when my ex and I got engaged.) It really solidified on 9/11.
I don't think I ever "turned" Atheist. We are all born atheists, and are taught religion. I never accepted the evidence, so .......
I second that