Compare two people, with different lifestyles:

Sam consistently works out twice every week. The exact workout he does
isn't important, but say he does 20 minutes of aerobics and 20 minutes
of strength training on each workout day. He is now 60 years old. He
has been following this general sort of workout program since he was
20 years old.

Jake has the exact same workout plan as Sam. He is also 60 years old.
However, he has only been working out since age 40. Before he turned
40, he rarely did any exercise, so, when he started working out at 40,
he was fairly out of shape.

At age 60, will Sam be in significantly better health than Jake
because of the exercise he did between ages 20 and 40? Can he expect
to live longer than Jake, and, if so, how much longer?

Double blind studies on humans are costly and subject to error,
especially over the 40 year period you suggested. My guess is the
exersize between age 20 and 40 typically adds only a few days life
expectancy at age 60, but it does increase the probability that you
made to age 60 in good enough health to persue a typical workout
program. Many other items in life style cause improved or reduced life
expectancy, so the exersize is more effective if most of the other
items are optimised.
 While you suggested that the workout details isn't important, I
suspect that the details can make a considerable difference in health
at age 60 and beyond. Many exersize buffs over do the exersize
occasionally and this can offset the good done by prudent amounts of
exersize.   Neil

Hello gremlin,

I can't find an exact quantitative answer to your question.  This
article from Life Extension Magazine, February 1996, Can Exercise
Extend Lifespan? by John Abdo provides some information
http://www.lef.org/magazine/mag96/feb96-fitness.html