One long-term solution is the following: - Everyone pays for their parents in their old age. - If you want people to pay for you in your old age, invest in ch

One long-term solution is the following: - Everyone pays for their parents in their old age. - If you want people to pay for you in your old age, invest in children of your own (by having them, raising them, etc.). - Or, you can invest the money you would have spent on children on yourself instead, or on your own investments. You are then responsible for yourself in your old age, no matter what happens. - Finally, we take a fixed percentage of the output of all working age people, divide it up evenly among the old people (who had children, weighted by number of kids)—and that's how much they get that year. If the children, in aggregate, earn more—old people are better off. If not, they're worse off (so do a good job raising kids, give them opportunities, etc.). This system is inherently solvent forever, since all old people that have children benefit from them in their old age—and those that don't, don't. It's literally impossible to have an "inverted population pyramid" or a "demographic crisis" with this scheme since all old people are accounted for.