I think I was 7-8 years old when I stopped believing. My family has a tradition of one of my uncles dressing up as Santa to visit our family on Christmas Eve. All the adults would gather us in the living room where "Santa" would come to the door to visit while an uncle would "go to the bathroom." It became harder and harder to believe with my older cousins having already figured it out and teasing us little cousins for believing. "Santa" still visits and now that there are little ones again (my nieces and nephew as well as cousin's children), it's time for the next generation to grow up with the tradition.