How to get into the Film Industry: Specifically Directing?

I am a really creative guy and I am currently going into my Senior Year of High School. Everyone asks me what I want to do when I get older and I never have a straight answer. I could see myself in Law or Business, but deep down I want to get into screenwriting and directing. People tell me it's unrealistic, but I want to know what it takes to become a big time director. What are good film schools and what are some things I can do now to prepare?