Wonderful article on the immeasurable value of walking as exercise. Like other writers, my ears perked up when I heard reference to "age 50 or older" as elderly, especially when life expectancy in so many countries in over 80. But I see what your meaning was here. I have a relative who started walking about 1-2 miles each day extra in 70s and was in excellent health in early 80s, still is going strong though slower in late 80s. Similarly, my parents are in early sixties(still young for sure also) and can walk many miles still at one time.