If you choose to attend college after graduating from high school, you'll be eligible for fellowships such as Boren, Gilman, the Critical Language Scholarship program, Freeman-Asia, and many more that provide partial or full scholarships to study abroad during undergrad.
Once you graduate, there are even more opportunities, especially in the field of English education. Programs like Fulbright English Teaching Assistant (E.T.A.), Japan Exchange and Teaching (J.E.T.) Program, Teaching Assistant Program in France (T.A.P.I.F.), and the North American Language and Culture Assistants Program (N.A.L.C.A.P.) in Spain all provide salaries and insurance for Americans looking for opportunities to teach English overseas. Princeton in Asia, Africa and Latin America also offers a variety of teaching positions that are not specific to English education, and you do not need to have attended or graduated from Princeton to qualify for these jobs. Peace Corps or Peace Corps Response is also an option for all ages, although they prefer you to have a college degree. They have 27-month contracts (or 6 to 12 month contracts for P.C. Response) in Education, Agriculture, Health, Youth in Development, Environment and Community Economic Development.
Whether or not you venture abroad in the future, you can still be a global citizen by taking the time to learn more about the world around you. By learning a language, making an international penpal, joining an international club, or simply cooking something for dinner that has roots in another continent or culture, you can contribute by having a sense of how you can make the world around you a better place.
Best of luck for your futures!