Rushing through the middle-to-high-school curriculum is easy. Very, very little novel information actually gets taught over the ~200 hours that make up a school course.
Rushing through undergrad is possible if you do nothing but grind homework and study and read.
Grad school requires you to spend hours and hours in a lab, ass-in-seat, doing research. You're no longer competing with beer pong champions. Unless you're an absolute genius at finding the right direction to solving a novel problem, you're not going to get dramatically better results than your peers. And even if you are, you might be unlucky, and end up wasting a lot of time going down the wrong rabbit-hole.