What you've described is the best-cast scenario of an aging population. Far worse is the modern reality in most places, which is systems that take growth and a

What you've described is the best-cast scenario of an aging population. Far worse is the modern reality in most places, which is systems that take growth and a certain demographic shape as base assumptions, and then make promises to people decades in advance based on those promises. That's what we do in the United States (and probably most places, but I won't speculate.)