What is the age of the youngest ATV rider you know? Our youngest rider was two years old. He was taking a ride with Grandpa. Grandpa saw a friend by the side of the road that needed help and stopped. When he got off the bike he turned it off but did not take the key. Junior turned the key on and, next thing Grandpa knew, took off down the road. While I really would have loved to have had a video of Grandpa chasing the ATV down the road, I could have shot him for not taking that key out of the ignition.