Oh man, don't get him in college yet. Baby steps!

Start with reading (language), mathematics, and basic physics. Get him to read young adult novels - nothing fancy, but that's not the point. They should exciting and easy to read. If he likes fantasy, I suggest Dresden Files and Lord of the Rings. They're lengthy and not too hard on the reader.

For math, honestly just buy a second hand high school textbook and answer book. Just work through that as fast as he goes.

Physics itself isn't important per se, but learning basic physics teaches you to think in a critical and analytic way. It's absolutely essential to have this kind of view if you want to start college.

And please, give him time. Support, don't push.