It's true that as a general rule, if you haven't revolutionized (or greatly impacted) your field by age 30, you're likely not going to ever do it.

However, that doesn't mean that the mind of people over 30 doesn't work as well. It may just be that people have different personality types, some people don't care that much about revolutionizing the world, and those who do care do not require all that long to do it.

So by age 30 or so, you're left with two self-selected groups: those who passionately wished to change the world and those who focused on some other priority in life instead.