I grew up in a catholic family, but I began to think there was something wrong in religion when they told me that Santa Claus was an invention. In this respect, why did I have to believe in god rather than in Santa? I wasn't able to understand it, so i started to call myself "atheist" when i was 12, despite being afraid to tell my parents i didn't believe in god anymore.
During my adolescence, after a difficult reflexion, I forced myself to believe, but I had to face even catechism teachers about Darwin's theories (being insulted with statements like "From now on I'll call you 'monkey'!"), and none has ever been able to give me a good answer about god.
In the end, after attending a religious group of young catholics (although being directed by honest franciscan monks), I realized that religion wasn't good for me.