The reason I like this article from Runners World is because it deals with the topic of athletes againg, and deals with the topic using real examples.

Here, the author, Ed Eyestone, discusses a professor he had in grad school who not only prosletizes regular exercise, but also lives what he preaches, and to great success. The professor is now well into his seventies and still maintains an active teaching schedule and still exercises regualrly.

How does he do it? With super fast interval training and active recovery.

Greater details can be found here: http://www.runnersworld.com/article/0,7120,s6-238-263--12898-0,00.html

Highlights of the program are below:

Fast and Active

For this workout, keep the intensity high on the intervals, and in between jog at a pace three times slower. So if you run your 400s in 70 seconds, jog for three minutes, 30 seconds. Do any of these workouts in place of regular speedwork once every two or three weeks during a training cycle.

Workout: 14 to 16 x 200
Interval Pace: 5-7 seconds slower than all-out pace
Recovery Pace: 200 jog at 3x slower than interval time

Workout: 10 x 300
Interval Pace: 7-10 seconds slower than all-out pace
Recovery Pace: 300 jog at 3x slower than interval time

Workout: 8 x 400
Interval Pace: 10-15 seconds slower than all-out pace
Recovery Pace: 400 jog at 3x slower than interval time