Voluntarily or not, many people 50+ are thrust into retirement but have job juice left and so turn to self-employment.
Some such people do what they did but only on a consulting basis. For example, a human resources manager who specialized in race and gender compliance issues might help various organizations with that.
But if you want to start a new business, it's usually wise to choose one with few moving parts and that requires little money so you don’t run out of cash before your business takes off.
Here are some simple, low-risk businesses well-suited to older people: