I started at about age 8 or 9 with a Yamaha 60cc 2-stroke dirt bike. Then, when I was 10, I got a Honda 75cc 4-stroke dirt bike, which I loved. It had a lot of grunt for a little thing. I knocked my front teeth out on the Honda, doing a hill climb, before those foam tube pads for the crossbar were very common. Nobody at school had believed I had a motorcycle until I came to school Monday morning with no front teeth.
Around age 14 or so, I got a Kawasaki 175cc 2-stroke dirt bike. I rode that a lot with a friend of mine, on his farm, until I went to college. I dislocated my shoulder on that one when I got into a cow rut and the bars caught in a fence I was riding next to, trying to cut off some escaping cows we were herding. That was a fun bike to ride, but I think I like 4-strokes better. More low end works better for a heavy rider. I left that at my parents' house for a long time, and eventually I gave it to my nephew.
I never raced, or anything, but I was a decent rider - accidents to the contrary.