Majority of F1 and NASCAR drivers today started out in a kart at very young age. Alonso is reported to have started karting at the age of 3, Jeff Gordon and Tony Stewart both started karting at a very young age. By no means does this mean that you shouldn't start karting later in life, nor does it mean you have to be a male karter. Many female kart drivers are very quick, partly due to there size but mostly they have what all race drivers have which is desire. The will to win and will to learn are the most common attributes to becoming a really good kart driver no matter what the age.