Rannoch Donald helpfully pointed me to this article The Shape of 40+ : The Science: Riding the Storm - which has some great insights into the maintenance of fitness and peak performance as we age.
..........older athletes don't perform as well as they used to partly because they don't train as hard as they used to. They work out less, in turn, not because of bodily limitations, but because of psychological and societal factors. At this point, the contradictory knot starts to unravel: While age-related physical decline from peak performance stands as scientific fact, athletic extinction proves to be a layered story open to a host of culturally influenced interpretations and different endings.
It is a useful and inspiring read with several good insights like that.
Also related to these ideas, a regular reader and commenter Dave C - who maintains a nice blog recording his quest for fitness - highlighted the case of his wife.
She is 63 but - as you can see in the video below - she is one tough Grandma! 6 chins, 15 dips and 11 feet elevated pushups in 2 and a half minutes. I bet there are lots of people 1/3 of her age that can't do that. Fantastic!