This is a uniquely American question. In all the rest of the developed world, your universal health insurance covers your medical expenses regardless of whether you retire early or not. In Canada, this is “free” at the point of service, i.e. paid for by taxes.
When I reached 65, the provincial government in Alberta topped it up with additional insurance coverage including prescription drugs, diabetes supplies, ambulance services, psychological services, home nursing care, and chiropractic services.
I paid more than enough in taxes when I was working, and that paid for my parents, but now since I retired someone else has to pay for me. Well, actually I still have to pay taxes because my self-directed retirement plan is overly generous.
In many other countries, coverage for seniors is even more generous than in Canada, so the correct answer in countries outside the US is that the government pays for your health insurance after you retire, regardless of age.
You mileage in the US, of course, differs from the kilometres used elsewhere (except the UK but lets not talk about that.) The big difference is having a universal health insurance system for everybody, including people who have little or no income.