Medicare is a Federal program. It doesn't go bankrupt just because people put less money into it than what they draw out of it, as long as the Federal government handles the difference.
Number of old people doesn't really matter; the danger that is facing much of Europe and Japan is that the median age is going up leaving insufficient numbers of younger generations to cover their pensions. Typically, states are planning to pay pensions from future taxes. If younger people are impoverished by the recession, its still only a minor issue for they will grow more prosperous as the economy grows stronger. No recession lasts forever. Furthermore, I was under the impression that thanks to immigration, the median age of US is not growing old!
Entitlements are good for the cohesion of society. Even in the socialistic paradises, the Scandinavian countries, they are not large enough to make a significant amount of population live off nothing but benefits. You need to be a very small-minded person to be satisfied on that level. But they are enough to ensure that nobody starves or has to live in a cardboard box on some back alley or that no-one dies because they cannot afford proper healthcare in a timely manner. They don't really take away your free entrepreneurship or responsibility - they provide a safety net for the rainy day.