I rode my first motorbike at age 5 when I got all of my older brother's hand me down models but hey I didn't mind and THANK YOU MY DAD!!!!! I had trail/enduro and dirt/moto-X bikes my entire childhood, I grew up or atleast got older anyway and didn't ride for 25 years. I hopped on my first motorcycle last year and rode off like I never missed a day of riding. It sticks with you like 2nd nature. If I had a kid I would keep him/her ready to ride, I know several fathers out there my brother included that really got to bond with their kid while out riding off road somewhere. It get's them ready to be a great motorcyclist if they choose to ride later in life. Then they can grow up like me and run from the LEO's at 170 and you can be proud of them. Well just kidding.
I started riding at 5-6 years old. Had my AA license by the time I got out of high school. Got my son his first bike at age 7. Just bought him his fith bike a YZ250F for his 13th birthday, so he would stay off my 450.
I started at around 8(?) My great grandma was a rider until about 75 years old since they lived out in the woods and had to ride horses or motorcycles to the town for groceries. Her children said enough and sold her bike and hired someone to run errands for her. My favorite was a greenHonda cub that she owned. After that, my cousin got his hands on a Yamaha DT125. Boy did we have fun on that bike. He still owns it and is his main transportion back home. I have to admit that we didn't wear any gear and our parents where ok with it. If you crashed all they would say was, "ohh you'll be fine" and rub some lemon and salt on the scrapes. That was some painful stuff. Ohhh, How I miss riding down to the river through the mountains and spending the day trying to see who could swim across the river more times. That was a fun simple life. Lol!