[ta0987]

Paying for retirees is solvable by simply aggressively taxing the billionaires.

You can't eat money. The problem is not financial, it is economic. Ignoring the few durable things that can be stockpiled, the money retirees spend, whether it comes from savings or taxes can only be spent on goods and services produced at the time the money is spent, by the labor force available then. The smaller this labor force, the higher the wages, the less purchasing power money has. Retirement saving becomes a positional good, it's not enough to save enough, you have to save more than the other retirees, because you're all competing for the same scarce resource: labor.

If that doesn't make sense, try thinking about it from a purely physical point of view. Retirees need physical goods and personal services (e.g. nursing). Both of these require humans to produce. The fewer producing people there are (young and middle age adults), compared to consuming people (retirees) the less there is per person, regardless of who you tax or how.

[nradov]

We kind of can eat money. Agriculture is already highly automated, and will become even more so as labor costs increase. For example strawberries are currently picked by hand because the fruit is so fragile, but picking robots are in advanced stages of development and will probably be widely deployed within a few decades.

A reduced supply of younger workers will also tend to increase retirement ages and reduce age discrimination. For example, a healthy 75 year old can still do a lot of nursing tasks. He might no longer be physically capable of lifting a bedridden patient but he can administer medications, record vital signs, change dressings, etc.

[ta0987]

I mean, sure, kind of. But indirectly. We can eat improved technology which we might be able to buy some of with money.

increase retirement ages

Yeah, that's one of the negative consequences of the demographic collapse. Not that old people who can still work are owed a vacation funded by the young, but the world isn't exactly fair in handing out pain, and not everyone who can't retire will be deserving of not being able to retire.

reduce age discrimination

Maybe. Old people too broke to retire don't have tremendous leverage in the labor market, and historically market forces don't tend to fix discrimination, see, e.g. Blacks in the US.