Seminary, studying the bible and religious history.
I had also had doubts about religion. Whenever I went to church the stories did not resonate with me and I found most of the people to be either inauthentic or just plain weird. Then, one day I bought a book....."The God Delusion." That book had a profound impact on me and I spent the next few years devouring ever book or article I could find on the topic. It has been a very rewarding journey for me!
I always was because my parents wer,e and it isn't of any interest growing up with something unimportant - that doesn't impact your life in any way - its a non issue and for me always has been .the idea that you might ever need a god has been so far out of my consciousness as to be of zero interest. I have mostly met friends who were also atheist but I do have some religious friends but we seem able to laugh about it all - I often get called the wee heathen and I don't mind that at all.