The most important thing for a school age kid is to become well-socialized.
The correlation between skipping grades and turning out well is just a correlation - it may be that those who were not allowed to skip were so messed up socially already that they were less likely to convince their schools to let them skip grades. In contrast, if you're well-adjusted and smart, it's more likely that you'd be able to convince school administrators to allow you to skip a grade. And, of course, Time misses that distinction, making it into a clear case of "the more grades skipped the better."