One other (bad) option is raising the retirement age or lowering the start-work age.

Maybe the solution is simply to end retirement. As in end the social security for old people.

It’s already set high enough that the years past that point aren’t productive. Social security and Medicare/Medicaid were a response to advanced age meaning destitution, poverty, and horrific suffering.

It’s essentially UBI and universal healthcare that winds up making a lot of demand for younger workers. Keeps the grandparents able to help raise kids, if wanted/suitable.

Maybe we could also recycle old people into fertilizer to decrease reliance on fossil fuels.

Once we have robots doing most jobs, heck why even have babies?

> until we have robots which can fully replace many/most jobs people do

Most people's jobs aren't necessary for a functioning society. If you look at say, agriculture, transportation, energy, sanitation, infrastructure, etc, what percent of the total population is employed in those fields, 5-10% maybe?

Society will be fine for a long time with drastically dwindling population, we'll just see a contraction of the "bullshit jobs" which have become the mainstay of post-industrial societies, with a higher percent of people employed in fields which are actually producing something of value for society.

What we need is a Agricultural Revolution in the Health sector. As it stands, it is way too people intensive.