Once you retire it's very difficult to go back to work. So, there are many out there who prefer to work well past their late 60's. Now, should they be working full time at that age? I can say most Anesthesiologists start to scale back at around 62-66 depending on their financial condition. Those who have spent a lot or gotten a divorce or just like to live high on the hog may need to keep working. A select few are wealthy enough to fully retire. Many choose the intermediate path and work locums or part time so that they keep up their skills but have plenty of time off with reduced call burdens (no call even).
I think a lot of SDN members will be in the intermediate/middle group vs the FIRE group who fully retire before age 55. I think anyone retiring before age 55 is indeed FIRE as most of use don't start earning significant money until around age 30.