Who will pay to care for the aging population? Welp, whether you live in a socialised care country or the United hellscapes of America, the answer is: you will. Or your kids will, or whatever generation we're talking about here.
Even if you do live in the US and have no elderly relatives, the insurance companies will have to hike the shit out of their premiums to remain profitable.
The fewer working age people there are compared to people past working age, the worse it will be.