Besides the age requirement, you must also be 5 feet tall. I didn't know about this - on our last trip to WDW, my dd's friend, who was fourteen at the time, was barely 5 feet tall. I had purchased the family plan at Carribean Beach, and the first day they had no problem. The next day, she was told she couldn't drive. When I had signed up they were both with me and she was never measured - they immediately used the mice. When I questioned this the next day after she was told she couldn't drive, they remeasured her and noted on our card that it was okay for her to drive. She really was 5 feet tall - it just depended on which CM measured her.