> going to be one of the grand challenges of the 50 years

I’m sceptical of this claim. Demand per capita grows unabated. Working lives are lengthening. A smaller population living well is economically indistinguishable, in the aggregate, from a large one living poorly. Maybe post-industrial civilisations settle into a lower-population steady state than ones requiring lots of unrefined labor.

Yes, dependency ratios will mean re-jiggering the skewed benefits almost every country provides its old at the expense of the young. But that, too, isn’t a bad thing, particularly if it encourages labor force participation.

(There is another comment arguing demographic the dividend’s inverse is a myth. I don’t go that far. I just think it’s a manageable problem versus a catastrophe.)