Twenty years old? It didn't occur to me to start thinking about things until my later 40's. The problem of human suffering started my questioning, and then that led into questioning in all sorts of different areas - history, archaeology, geology, medicine, biology, etc.

Before that, I had moved away from Christianity because of the problems with the various denominations, as well as a way to explain needless tragedies that occur - I became a deist. Then I realized I was just creating my own belief system, with no foundation whatsoever, just in order to be able to have belief in my life, and I realized that was completely dishonest.

One thing you will find is that the longer you examine it, the more you see just how poor the arguments are for it. Think about who assembled the Bible - superstitious ancient Romans. The stories that comprise the Bible were selected to tell one singled story. It has a beginning (Genesis), a much longer middle, and a brief end (Revelation). It was meant to be taken literally. However, due to archaeology, medicine, history, science, etc., some things were shown to be wrong or fabricated, so that now parts of the Bible are taken to be metaphor/allegory and not true at all.

As you think about that, over time you come to wonder how you could have believed it without question for as long as you did.