Great thread. It's been interesting to experience my parents vs. my in-laws and their respective approaches to retirement.
My parents were both very active. Mom has lots of community volunteer work, participates in every neighborhood group imaginable. When she retired 10 years ago, it seemed as if nothing changed. My dad retired six years ago from a C-suite job at a Fortune500 company. He didn't really have any hobbies, activities, etc when he retired. t suspected he'd miss business and start his own gig. He consulted for 2-3 years, then hung it up completely. Since then, he's absolutely kept himself busy. Joined a band (was and still is a kick ass drummer, older than all the other members by 20+ years), helps my mom in some of the neighborhood groups, and we just recently bought a ranch in Kimble Co. They're busier now than they were when they both worked. Both incredibly healthy.
My FIL retired from his full-time job last year via a forced retirement / severance. Literally came out of nowhere and he hung it up with about one week's notice. Still has a side business that he runs, but he hates it. Ready to sell it. He spends the majority of the time at his lake house just hanging out. Fishes some, but not much. Health has already started to decline in that year since he hung it up. MIL has now pushed back her retirement four times in the last two years. Latest was from July 1 to March 1, 2019. I think it's because she doesn't want to be stuck with the FIL all day. There's also no other activities and she's scared of having some extra spending money.
Just two very different situations. The best way I can summarize it is proactive vs. reactive retirement. I don't think it's smart to retire unless you have a game plan and know how you want to spend your time.
As someone who's self-employed, I don't know that I'll ever retire. I can totally see myself working 20-30 hours/week as long as possible even if I am "retired". But, that's still a long ways off.