Joe Henderson writes about running and life in books and as a columnist for Runner's World magazine. He also publishes a weekly commentary which you can subscribe to by email. Joe has been around long enough that much of his writing is about older athletes.
For example, the current commentary is on author Paul Reese who ran into his 80s. Another commentary is a tribute to George Sheehan who ran competitively and wrote eloquently about it until age 74.
(It seems that some old runners are also inspiring writers. Does running induce reflection? Do thoughtful people tend to turn to running for exercise?)