I think it helps to live in a city. The cities have their problems, they're expensive and dirty, but there are loads of older single adults, and even an introvert can sit at the same bar once a week and meet people, or go to meetups or a weekly class and slowly meet people. Hell, in bad times even chatting with a bartender was nice.

Being in your shoes in a suburban setting surrounded by families and neat little houses (or huge fields in a country setting) I imagine is hard. I'm only making assumptions.

Have you thought about traveling long weekends or abroad longer? Perfectly doable solo.