I have never understood how this is a "bomb," western cultures are so good at distancing the elderly, nobody will notice if conditions in care facilities become worse. How exactly will all of the unsupported old people overthrow society? By selling their IRAs? Will China's over-working-age-population get a second wind just long enough to take down the Party?

I think realpolitik has so permeated our way of thinking that an impending moral crisis or holocaust can only be brought into discourse as a nonexistent threat to stability. If there's any explanation for why people think an inverted population pyramid is an economic crisis, it is that their hearts are in the right place.

> I have never understood how this is a "bomb,"

Because it’s taxed working adults who pay for entitlements like social security and socialized healthcare programs. When retirees outnumber them, these entitlement programs will collapse. As you’ve alluded to Asian culture, these entitlement programs are even more important in Western societies because multiple generations do not live in the same home. Also high trust societies tend to have much weaker family links.

> How exactly will all of the unsupported old people overthrow society?

They are reliable voters. You can already see this in play in places like Japan. As for places like China, they just won’t have enough workers and soldiers in the long run. Yes, their economy is terrible at the moment, but nearly everything is cyclical. Also the younger generation will just see how the elderly are treated and will lose more faith in their government.

if the majority of the public is much older they will likely vote for measures that favor them. Millennials look like they will be pretty left-leaning. The US could divert 10% of its military budget and ensure seniors live in relative comfort.

I’m not saying these things will come to pass, only that it isn’t obvious to me that there is a coming crash. The economy will morph to reflect the forces that exist within it.

There is a huge debt that the military budget might be diverted into instead. It's likely this military budget that ensures the debt can be never repaid.

US federal debt can't just be "repaid", it's basically all in non-callable bonds. It can be paid on one schedule, and diverting funds to it won't get it paid any faster.

If there is enough money around for that to be possible, I don't see how people could call that a crisis.