Nobody starts the road to Formula 1 working on a pit crew. Most modern F1 drivers have been driving since the age of 8 to 12 in karting, progressed to junior open wheel cars, and advanced through F3 or GP2 to F1.
Which is really along the same lines of NASCAR in theory. Midgets - ARCA - Trucks - Nationwide and then the big league. It doesn't always follow that anymore. I would assume F1 is about the same way. I think attitude goes a long way as to which circuit they end up in.
He said it! Start with carts, win. From carts you go to the entry of whatever league you want to progress in. No matter what series a driver is winning in he./she got there by winning the previous step on his/her path.
How about the young drivers that get into F1 racing, how did they get into the race when they are so young? Can you pay your way if you have the money to be able to race in F1 competition?