3 options:
1. Join the military as a pilot, be at the top of the class, put in long and hard hours for several years, and if you are lucky and the right people like your personality, they will send you to test pilot school.
2. Get an engineering degree in something applicable to aviation, become an expert in that field, get a job with an aircraft manufacturer, and if you are really lucky and the right people like your personality, they will send you to test pilot school.
3. Save your pennies and when you get to about $500 000, ask the test pilot school if they have an opening.
Oh, by the way all three options require you to be able to read and write to a high standard.