Saving up your entire life to buy a Mustang is amazing for a 16-year-old. You’re certainly a motivated individual.
However, you may have some alternatives. If you can wait two years, you can get a car loan. Judging by your savings rate, however, you might even have enough money to pay cash for the car by then.
Alternatively, you can buy a used Mustang for cash. If you buy from a dealer, the dealership guarantees the mechanical integrity of the car through a warranty, which might be a better option than buying from a private seller who offers no promises or warranty.