Comment by disgruntledphd2

> Once a society enters sustained low fertility and longer life expectancy, each cohort is smaller than the one before it.

I mean, unless fertility completely collapses (to like less than 0.5) then it'll mostly be a single generation problem. Regardless of any future changes, the current generation (my kids etc) will be supporting a much larger older cohort, with problems arising from that. I am one of 4 siblings, have two kids, and as long as both of them have two kids, no more problems arise (obviously extrapolating to the population).

There's some amount of irreducible demand for kids so I'd be surprised to see TFR continue to decline on a generational basis. Mind you, I could be wrong (or alternatively, we could see a massive increase in TFR like we did post WW2).