I think he's, like, totally not saying "I want to" or anything like that. AFAIK he may deeply love under-120s.
He's just saying that the world is overpopulated and without a dramatic reduction, we destroy the planet. We'll destroy our inheritance and natural resources for no gain but saying "we supported 10 billion people who didn't do anything for a while, yay!"
It'll be like Easter Island, but this time the Island is Earth and there is nowhere else to go and no other humans surviving elsewhere. Everyone will die because we couldn't rise above the animal instinct to over breed or even come to a basic consensus on survival. Nature is supposed to keep us in Czech, but instead we rose above it and in doing so destroyed it.
Shit sucks no matter how you cut it.