The key single item in retirement I think is being able to walk (aside from brain issues). If you can walk, do it, a lot, as you age. Retire some place that encourages you to get out and about.
Like everyone, I see folks 80+ out walking, at least slowly, and they can manage pretty well, and others maybe 65 or less, who may be obese and using carts to navigate Walmart etc.
Obviously some stretching and light resistance work is also great.
