The traditional approach to this is:

a) make younger female family members do all the work

b) make them invisible, politically and socially, so everything looks fine

As an aside, I haven't seen a street being swept in my area in nearly 25 years.

Forms of retirement that don't have the force of law can be adjusted on the fly to match the available resources. When the government forcibly requires that each elderly person be paid a fixed amount of resources yearly, it's possible for there to be literally zero surplus for the young people making the resources. That can't happen under systems where the transfers are voluntary.

> I mean, who else going to grow the food and sweep the streets?

I'm not sure what the state of the art is with either of these, but I'm now imagining scaled-up Roombas stealthily cleaning the streets at night.

Or this, but self-driving: https://www.alamy.com/compact-kubota-bx2350-street-cleaning-...

More seriously, I think there is a before-and-after point with AI, before some point the automation is just a "normal technology" and we need humans for a lot of jobs, pensioners can only get meaningful pensions when a new generation is present to pay for it all, otherwise pension ages need to keep rising; after that point, automation is so good we can do UBI (AKA "set the pension age to birth")… well, provided the state owns the automation, otherwise good luck demanding free access.

(I am a social democrat, not a libertarian) All models require to some extent the youth working, but not all require a part of the youth's fruits of their labour being taken and put into social security. A libertarian might say that the onus is on the boomers to save enough money to fund their own retirement so that they're not reliant on the social security safety net.