It is a highly ambitious dream to follow, but never lose hope. There are opportunities aplenty for budding astronomers, as the field of astronomy is a relatively young one and thus, has thousands of career options.
You may start with working hard. Whichever country you may be from, astrophysics is taught at the premier institutes of that country (ISRO in India, NASA in the US, etc. ) hence you need very good grades for that, especially in physics and math.
You may start by observing the sky. Yes, it's that simple! :-) Noticing new planets, stars and other celestial bodies IS the basic building block of astronomy - the more you observe, the more you learn!
You may also check out the webpages of famous astronomical societies if you want to know more regarding astronomoy as a career. They do offer a lot of programs for school children, which may give you just the push you need in the right direction.
Give the steps!