Im 16. How do I get good enough to race in the Indy Racing League?

I'm racing go karts everyday, around my streets mostly, but its practice. I'm trying to save up enough money to buy a spec race car. But thats the thing. What league should I get into? Legends, Enduro, I really dont know which is the best way to get noticed. Im pretty sure I have to get noticed by nascar first then indy. Any help is greatly Appreciated. Thank you.