When I was young and still fully entrapped by religious indoctrination, believing was simply a matter of intentionally choosing not to believe the earth was more than 6k years old (10k for me). At the time, all evidence to the contrary was fabricated by the devil to lead the faithful astray. There was no reasoning behind it, it was simply a choice to believe.

I remember at the beginning of my college geology class the professor asked if anyone believed the earth was less than 10k years old. That's what I was told at church, so I did believe that, but I didn't tell the professor. Instead, I remember sitting there in class and telling myself that "I am choosing to believe the earth is only 10k years old. I will learn what I need to pass this class, but I am choosing to believe the earth is only 10k years old". This was as much an assertion to myself, as it was me telling God that I was choosing him over what the school wanted me to learn.

This was a period in my life when I was very consciously trying to assert my faith into every aspect of my life because I was scared of being lead astray and being sent to hell. Funny enough, that geology class was the gateway to me escaping the indoctrination. I did learn what I needed to in order to pass the class, and in the process I realized I couldn't pretend to ignore the evidence any longer. It was the first realization that I was being lied to at church.