How prodigious do you have to be for society to push you along like this? I accelerated a lot, because I wanted to get to the good stuff, and I felt burned out occasionally when I did too much pointless work unrelated to what I liked, but otherwise was fine, even in the heavier semesters.
Basically, I figure there are two reasons to accelerate. One, it's dumb to waste time on things that don't matter (like the two years of high school math over which are distributed about six weeks of material, also known as algebra II and precalculus); you wouldn't want to waste your life in high school any more than you'd want to waste your adult life.
Two, you have only so many years of real productivity, I'd say between about 18 and 39 (upper bound varies by field and individual), and you want to spend as many of them as you can doing real work that has an effect on the world, rather than education.