I'm sure there are some people that can keep themselves happily busy, but I've seen these kinds of threads about early retirement come up now and then in different places and always its the same: people who have not had a lot of free time incredulous or even seemingly offended that anyone would be happier working, and then many accounts of people that actually retired early saying it made them bored or depressed.

Alternatively, I've taken a year+ off multiple times in my life for "funemployement" and I was quite antsy and bored and restless but also lacked motivation to do much. I think it depends on the person.