The world is run by people over 30 and us over 30s know it. That we don't challenge the conventional wisdom that wonder kids are disrupting everything is just a demonstration of our secure confidence.
I tend to read that wisdom as referring to things like mathematical theory being mostly advanced by people under 30. People's brains seem to hold onto some extra bit of IQ between 20 and 30, that can be used to do some "wondrous" things. Of course, most big things that need doing don't need a supergenius; they need 10-20 years of steady hard work, so by the time you accomplish those you are indeed 30+ (or, god forbid, 40+.)