At 14 you have no idea what you'll want to do in 4 years time. I promise. Also remember that the world of design will have changed a lot by 2017/2018. Great that you're getting started so early. Just remember to have fun, and don't take things too seriously.

I personally prefer designing for the web, but some of the best design classes I took weren't necessarily "pure design" classes. Photography taught me how to make better compositions, bookbinding taught me how to prepare work and think several steps ahead, and Letterpress taught me how to better work with type, and understand how tiny things come together to make something overall great. While whatever college you may choose will probably have some kind of step-by-step degree program, don't forget to explore outside it some. Who knows what other classes may teach you.

Here are a few online classes / resources to explore:

https://www.edx.org/course/harvard-university/cs50x/introduction-computer-science/1022

http://www.skillshare.com/classes/design

http://www.skillshare.com/classes/design/Intro-to-Web-Design-Friendly-Design-for-Startups-and-Small-Business/1922806972?via=homepage

Figure drawing. With live models.

Often good design has the same basis as good art. Composition, contrast, communication. Those can be learned in drawing, photography, and other traditional art classes. It's best you learn from the masters right now about the theory and practice of creative composition. That applies to any kind of design. If you can find a typography, print work, or writing class those will be really helpful. Also at 14, you are in a perfect place for the 10,000 hour theory. To become a master at something, you need to spend at least 10,000 hours (7 years). Find the thing you love the most and do it over and over.

I don't know how it works is the US. In the UK I would recommend graphic communication then in your final year master in the area you like most. Typography is always a valuable class. Then take photography as a night class and in between all of them teach yourself coding with something like Treehouse. Oh and don't forget to have some fun ;).

I definitely think cross-disciplinary design is the future but I can't say many universities have caught on. Schools tend to restrict design classes to specific majors so an industrial design student wouldn't take typography. However, that doesn't mean you can't or shouldn't.

If you aren't sure what design discipline to focus on then just start making stuff! Build a webpage, sketch a product design, make a poster, etc. You'll eventually find your calling.

Good luck!

I'd say some "boring" classes like Color Theory or Art History are really handy and most of current designers lack that education. I believe they are very important to train you visual baggage/taste

As a graphic designer with about 5 years of professional experience, currently in his 2nd year of an Information Design degree:

Take business classes.

Can anyone recommend some online classes?

I have a full time job and going back to college isn't an option. We have evening courses for adults here in Belgium, but none of them seem to educate graphic design on a college level. It's really frustrating.