I've been into professional football since I was about 4, and for a few years, the Green Bay Packers were my favorite team. But from since I was about 5-6 to now I have been a Bengals fan (local reasons).
I started watching basketball at about 7 years old. I liked the Cavs because they were the only team in Ohio, but about a year later I started liking the Celtics b/c there is no basketball team in Cincinnati (anymore). I didn't watch baseball until I was 10-ish, and I've always liked the Reds the most.