How do you become a professional NASCAR driver?

i mean you do you start out at, i supose you have to win some amatuer races n evrything but how and where and when? i know theres a lot of you NASCAR fans id appreciate the help and does it cost money?

what is the average age to start training for nascar, to become a professional?

What is the average age, of really starting to get into the sport, of all the nascar great. At what age did most nascar greats start training to become a professional?