I had reached 66 1/2 and we had lived a rather frugal life, so my younger wife and I thought we could do OK if I retired. However, there were three other, more pressing reasons that persuaded me it was time. First, I am a polio survivor (iron lung, hospital for almost a year, wheelchair and braces, multiple surgeries throughout childhood), and although I'm doing very well considering, my "cohort" doesn't have the greatest life expectancy. Second, for all my physical (and perhaps mental?!) limitations, I'm an avid backpacker and as post-polio syndrome seems the norm for us, I still have trails I haven't packed and rivers that I need to paddle before my circle is done.
But the most important reason I retired was my position at the university. I loved teaching and was always ranked among the top by my students. But four years before I retired I became department chair. Hard to admit, but this was not a skill set I excelled at. I would spend a whole weekend working on a proposal for funding or position we needed, and my fellow chairs in the college would write up theirs in an afternoon. Theirs were notably better than mine, so for the good of the department, I thought it best that I would fade out. If you have ever worked hard at something and realized others were doing it better in less time, you know the feeling.
My only advice to those retiring is to take future commitments slowly. I got bored and joined the American Red Cross, Arkansas Master Naturalists, a variety of other civic-type organizations, and recertified my state referee license. Suddenly I'm busier than when I had a paycheck coming in!
Natch