I stopped believing at four. I had serious doubts that a person existed that I couldn't see and had to take someone's word for. I saw the toys under my mom's bed that were from "santa". I asked my dad who always told me the truth and asked him at four years old if Santa was real. He asked if I believed in him and I said that I didn't think he was real. My dad then explained that he was a real man in Germany a long time ago who gave gifts to poor kids, and we play Santa because of this man. He said it was to remember the spirit of Saint Nicholas. I was pretty happy with this explanation.