I think he's full of crap.
There are plenty of younger bands out there at arena and approaching stadium level. The problem is that the live music industry, particularly for rock and metal, is stuffed with much older bands, most of whom should have retired long ago.
I mean, even fucking KISS, who just played their "final" show refuse to just fuck off properly.
And the festival organisers are afraid to put younger bands on as headliners for fear of scaring off the oldies who's disposable retirement income they rely on. Because they've created that expectation that there's going to be a Maiden or Metallica playing every year.