The minimum age to race in the NASCAR Camping World Series (East and West) and NASCAR Whelen Modified Tour (North and South) is 16. Otherwise, you have to be 18 to race in the NASCAR Camping World Truck Series, NASCAR Nationwide Series, and NASCAR Sprint Cup Series.
The drivers must reach the halfway point of the scheduled amount of laps in order for a Nascar race to become official. For example, if it's a 200 lap race they must complete lap number 100. Once they begin lap 101, it's an official race.