Depends where. A lot of first world countries don’t want to import more old people who will be a burden on their health care and other social services, especially if they suddenly find themselves poor and have to rely on the state.
So the first and obvious question is, what will you do for health care? Does Medicare actually cover people who ahve left the USA?
I know a number of people in Canada who had to give up being snowbirds when they could no longer afford the travel health insurance due to age or a new condition.
A friend’s uncle was found in his Arizona trailer with a stroke, unable to move - foolish guy had no health insurance. His buddy drove him non-stop back to the Canadian border so he would not go broke down there. A retired coworker was unable to go south for 2 years when she had a heart problem and nobody would sell her (affordable) travel insurance.
OTOH, for relatively healthy types, fredoneverything.com mentions in asides in his blog/column, the health system and other amenities of living in Mexico are just fine for him and quite affordable.
Americans are required to complete tax returns no matter where in the world they end up. You probably don’t want to mess that up. You don’t want to discover that your pension and bank account have been frozen in the USA because of some difficulty you had no clue about if the mail did not reach you.