Interesting... I am approaching 50 and have noticed a slight reduction in mobility. I have recently read articles about certain markers of mortality (or is morbitity the word here?) - like the ability to get up from the ground without using arms... or trying not to sit too much during the day. or trying to walk 10,000 steps (according to that dubious android app).
Particularly the 'idea of getting up from the floor without use of arms' made me think of certain simple motions that are hard for me. There is a Korean buddhist practice of 108 bows - I recently tried and got to about 25. (not just Korean - I should have said I learned it in a Korean context)
I am disturbed by the idea that there will come a day where I cant do "x" anymore, where x is running, drinking guinness or some other such activity.
Recently bought a block of training sessions at a gym and discovered stretching with the aid of hard plastic tubes or rollers that help stretch out areas of the body that are a bit hard to stretch otherwise. Hip flexors, trapezius (sp?), etc. This has greatly improved my mobility and has helped me do things which were hard to do before (shoulder presses, running) without pain.
Reading this article it made me think of how walking alone might not stretch out muscles in the same way as running (or swimming, rowing, etc).
"But researchers and older people themselves also have noted that walking ability tends to decline with age. Older people whose primary exercise is walking often start walking more slowly and with greater difficulty as the years pass, fatiguing more easily."
They don't explicitly talk about flexibilty and running but some form of stretching is somewhat implied. It might be interesting to see those possible correlations.
And I thought of the octo- (and maybe nono-) genarian Koreans who would briskly walk by me on the small mountains in Seoul on their way to a temple to throw down a few bows...