China has a gross savings rate of 45-50%. Current gen has saved for their future.

Money is an abstract representation of the labor of others. If there’s no one to labor for you then your currency is just paper.

Currency might also just be bits on a server.

I agree in theory with you. But you can 'bank' labour for later on. Building infrastructure (that will last) when you have a population bulge, means that the generations after can take advantage of that infrastructure, and have to do the lower amount of work, of maintaining it. This can go for things like education, investing in businesses, and generally any capital.

Of course you can also over build this capital that will never be used, but will need to be paid back (for example a local government pays to build a town that there are no people to fill it with) and the maintenance is too much, but you still have to look after the people who did the building.

You can over-build things like old age care. We still don't have robots to feed and bath old people.