I don't know what population-wide aggregates might look like. At least in Silicon Valley, there apparently are many people who have retired early and have the ability and inclination to express any dissatisfaction online in places where I might read them, but I can't think of any who have said things like "My life has been miserable since I cashed out my millions of dollars of Google shares and I have nothing to do with myself."

Retiring early means you have the money for doing a great many things, and you are still in physical & mental shape to enjoy it; Twain:

“The whole scheme of things is turned wrong end to. Life should begin with age & its privileges and accumulations, & end with youth & its capacity to splendidly enjoy such advantages. As things are now, when in youth a dollar would bring a hundred pleasures, you can’t have it. When you are old, you get it & there is nothing worth buying with it then. It’s an epitome of life. The first half of it consists of the capacity to enjoy without the chance; the last half consists of the chance without the capacity.”

And what factors enabled this early retirement in the first place? A motivated intelligent person (albeit with a bad appetite for risk and inability to cash out) can find plenty of rewarding things to occupy themselves with, like charity or education. Steve Woziak and Cliff Stoll immediately come to mind, but I'm sure you can name others.