If he can write a good application and gets great scores at his tests (which he should considered how above the required level he is now), he should get a good

If he can write a good application and gets great scores at his tests (which he should considered how above the required level he is now), he should get a good scholarship and knowing the material should get him noticed pretty quickly which will open opportunities to publish quickly at least in mathematics. Plus, he clearly is self-motivated and able to study by himself. University will give access to a ton of material and researchers. He should thrive. Given the opportunity, learning is rarely a wrong choice.