The good thing about the seniors class is that most of those folks have to be at work Monday morning and are a bit more sensible than some of the 15 year olds---that being said, I have also seen some brain dead older drivers , and some 15 year olds that are mature beyond their years. but , yes most adult classes start at 15 so that is most likely where you will be. Take your kart to the track, start in back for a week or so, ask questions of someone who looks like they know what they are doing, and stay around after the races and get some more seat time.