A finance writer that I like, William Bernstein, wrote an example many years ago that illustrates the problem of too many old people and not enough workers.
http://www.efficientfrontier.com/ef/103/hell4.htm
...Imagine, if you will, a desert island on which there are only five inhabitants—four workers and one older retired person. Each of the four workers does several odd jobs: growing various foodstuffs, building shelter, providing rudimentary medical care, and the like. The medium of exchange is coconuts. Every month, each of the four workers gives a few of his coconuts to the retiree.
One day, one of the remaining four workers turns sixty-five and decides that he, too, wishes to retire. If he does so, instead of each worker supporting 0.25 retirees, each would be supporting 0.67 retirees. Not only that, but the total GDP of the island would fall by 25%; so would per capita GDP. What do you suppose the response of the remaining three workers will be to an apparently healthy-looking colleague who demands that they support his idleness?
Let us further assume that the candidate-retiree has planned for his nonproductive years by accumulating a disproportionate number of the coconuts. In doing so, he has done nothing to increase the productivity of the island. Now that he must spend the coconuts, the island will find an increased number of them chasing 25% less goods and services. The result is a predictable bear market in coconuts and dramatically more expensive goods and services.
Worse yet, to the extent that he has planned ahead and saved, he sows social discord, for even if he himself has accumulated enough coconuts to counteract the effects of higher prices, he has raised prices for everyone else in the process.
This example was not arbitrarily chosen. The 4:1 and 3:2 ratio of workers to retirees is about what was the case in 1990 and what will be the case in 2050, respectively.
In an era when a small number of people lived past sixty-five, society could easily support them for the very few years they survived beyond that point. Now that citizens are routinely living two decades longer, it is simply not mathematically possible, let alone politically feasible, to expect each worker to support 0.67 retirees, no matter how many coconuts, dollar bills, stock certificates, or Krugerrands they save up in the meantime. It is also not reasonable to expect productive younger individuals to support large numbers of healthy older non-workers...
I’ve seen the claim that the first person who will live to 200 has already been born. So imagine how much worse your scenario is going to get!