A person can have all the money in the world, but if there is nobody around that he can hire to produce goods and services he will live like a pauper. Therefore, the only determinant of how well a country will weather an aging workforce is not how much money is in retirement funds, but the number of people who can be hired to take care of seniors and continue producing the goods and services that will make it prosper.
It was the traditional responsibility of children to take care of their aging parents. As a result, to ensure a comfortable retirement, people had the incentive to have many children who would volunteer their labor to feed and house them when they become unable to work.
Thanks to a confluence of factor such as the birth control pill, which reduced unplanned pregnancies, and the expansion of safety nets, which transferred social responsibilities from the family to the state, fertility rates in industrialized countries fell precipitously over the last decades. For instance, according to the the Organization of Economic Co-operation and Development, fertility rates in its member states have fallen from an average of 2.76 children per woman in1970 to a below replacement rate of 1.74 children per woman today.
As the state became increasingly responsible for the welfare of seniors, industrialized countries introduced policies to increase savings rates in order to build a large reserve of capital to fund their retirements, such as public retirement funds to ensure that workers have a minimum level of income at retirement. Most countries also subsidize private retirement savings through tax-free savings account or tax-exempt registered retirement savings accounts.
However, as with traditional societies, people, not money, are needed to take care of elders, whether they volunteer their labor through a social contracts or for a wage. This is because no matter how much wealth is accumulated, no goods or services will be produced without labor - money cannot produce food, lay bricks or perform surgeries but can only pay people to do that work.
Industrialized countries that will experience the steepest socio-economic declines will be the ones closed to immigration. Much like Japan, on the surface, their economy will look paradoxical. They will experience zero-to-negative economic growth as the number of workers declines, while simultaneously experiencing wage increases and falls in unemployment rates as retirees bid for all sorts of services like plumbing, housekeeping, medical care…
Overall though, conditions will deteriorate for both retirees and workers because there will be less production, thus consumption, per person. This will be reflected through higher prices and rising economic tension.
Although it remains unpopular in many countries, the only way to mitigate the impact of an aging industrialized world is through global migration. Seniors living in industrialized countries, especially the less wealthy ones, will choose to move to poorer countries, where labor is more plentiful in order to escape high prices. At the same time, industrialized countries will have to take in more immigrants from developing countries to play the role of the caretakers and producer of goods.