I was thinking of the long period of slow economic growth, long period of low interest rates, "chronic deflation", and few tools left by central banks to stimulate the economy. https://en.wikipedia.org/wiki/Lost_Decade_(Japan)#Legacy

A deflationary situation where, to put it in one way, the value of money increases as time passes (as opposed to inflation where the value of money erodes over time). Central banks would then try to set negative interest rates so that any (digital) money one holds can be continuously reduced to incentivize spending rather than saving.

<2 children per woman I would guess, I.e. a lot of old people but few young. Or maybe they mean the high government debt but low real stock market growth?