There are several factors to talk about. The FAA requires you to have at Least 40 flight hours, made up of specific things like cross country, solo, night...(more likely 55-65 flight hours), take a Written test and you must be 17 to take the final test we call the check ride.
Now most of the time a student can fly, weather permitting, 3-4 times a week. So, that's about three months if you are really motivated.