If you or anyone you care about is or will be elderly and is not financially independent, you should care.

This has nothing to do with capitalism; it's a resource allocation problem. We spend inordinate amounts of money on end of life care, and any changes are currently unacceptable to voters.

You're talking about age structure, but overall population age-structure can be adjusted by immigration flows, births, deaths, etc. My point was about the total population number.

You can imagine a steady-state population where the age structure is stable and productivity is high enough to sustain the retirees, trainees, and disabled.