Older adults taking up exercise or switching to a new form of exercise.
"I am a 90 year-old bodybuilder" in The Telegraph (2nd April 2011)
90 year-old woman finished her last marathon having taken up marathon running at 71 years of age.
"Last Dash for 90 year-old Athlete."
91 year-old sychronised swimmer - started at 70 years of age.
"91 year-old athlete."
94 year-old marathon runner in Edinburgh Marathon (2005).
"Runner, 94, finishes capital race."
Ida Keeling took up running at 65 years of age.
"95 year-old Woman Sets Running Record."
A few more here as related links to "91 year-old Lady Runs the Marathon."
101 year-old marathon runner, Buster Martin. (He was a PT instructor in the army so a bit of a head start. Guinness World Records lists the oldest man to complete a marathon as the Greek runner Dimitrion Yordanidis, aged 98, in Athens in 1976. He finished in seven hours 33 minutes. Martin has not been so listed due to the inability to confirm his age.)