I can throw in my retirement experiences: I taught technical theatre at an upstate NY college for 32 years, and was offered an early retirement option in 2002 at the age of 58. I loved teaching, but for a number of reasons, both good & bad, after assuring that I could afford to retire, I decided to take it.
While we did a lot of traveling during the summers prior to retiring, unfortunately, due to my wife's illness, we only we able to make one long trip after retiring before she was too ill to travel. I agree with all those that suggest retiring as early as possible. If you have plans for travel, etc at retirement, the longer you wait, the more likely it may not be possible. My wife passed away in 2010.
I currently travel more than I'm home, but even when home I have as much to keep me busy as I did while working. I do lots of volunteer work including photography for a number of organizations, deliver Meals on Wheels, teaching computer & photography classes at the local library. One of the more unusual projects is doing a fund raiser for the local animal shelter taking Christmas photos of "Pets with Santa". Lucky, I'm the photographer rather than the Santa - He usually gets clawed or bitten each year, and has held cats, dogs, pythons, ferrets, parrots, etc.
In short, the advantage of retirement is you can be as busy as you wish, have as many challenges as you want, but you do have to "do it yourself" rather than have an employer plan your life.