Shared pension systems require high birth rates. But you can't have high birth rates in a democratic society that allows women to be free and independent.
So there are essentially two solutions:
1. [Full liberalism]
Drop the shared pension system. Drop free healthcare. Let boomers pay for themselves.
2. [Full interventionism]
Force women out of the workplace and back into the home. Tax single women to hell. Make them legally and financially dependent on men, so that they're forced to marry and have kids.
Both solutions are completely out of the question in our modern democratic societies.
1. will never happen because old people are >40% of voters and will vote out any politician that threatens their privileges.
2. will never happen because our modern societies are based on egalitarianism and gender equality.
So there's no realistic way to solve he problem. Modern states can only postpone the collapse, by taking astronomic debts and cutting any social spending that isn't geared towards old people (neetbuxx: RSA, CPAS..., unemployment benefits, disability benefits, etc.).