Go to fashion design school. That's a great start. Once you have a degree people will take your talent more seriously. Plus it will lead to internships and jobs. Just find a fashion institute in your area.
If you can take college course, by all means do so. Otherwise, start sketching and sewing. Or, if you can't sew, get someone else to help you! Then start selling your ideas locally, but make sure you can fulfill all orders!