This is pretty awful analysis. It conflates aggregate statistics (e.g. GDP) with per-capita ones (birth rates, cost per child). And it's headline is a clear lie designed to draw clicks.

Demographic change is a real challenge, and all industrial societies are heading for that kind of cliff. Japan's is larger than most (but smaller than China's), and they are going to get there first. But this isn't the kind of disaster being posited. It means, broadly, that for a generation or so society will be burdened by a disproportionately large elderly population, and caring for them will require resources that we'd prefer to spend on other things. But eventually things will return to a steady state, just with fewer people. We'll manage.