William, Follow your dreams! One point of clarification is needed on the pathway, however. After you graduate from high school, you should go to college and earn a bachelor's degree in any field. I do not believe you can become a military Officer right out of high school and fly C-17's. Some exceptions apply, such as the Army's warrant officer program (if it is still available)?? Others "in the know" can probably give you more accurate info on the warrant officer program if you are interested.
Get good grades, stay out of trouble, play a sport to stay fit and also work in some extra-curricular activities that will look good on your resume. Any type of club or organization that includes community service will be a big boost. The future is yours to have!