If you turned 65 in the middle of the last century—in 1950—you could expect 13.1 years more of life if you were a man and 16.2 years if you were a woman. If you turned 65 in 2007, your remaining life expectancy was 17.2 (male) and 19.9 (female) years. So, in theory, that’s about four more years for everyone to run marathons and go paragliding.

In practice, for a lot of people, it means more time to lie around in a state of misery and sequential organ failure. New York Times columnist Gretchen Reynolds points out that chronic diseases are growing dramatically, so that a longer life actually means a “lengthening of morbidity,” which is actually horrifying, which is actually the most evil bait-and-switch imaginable: instead of four years of building Lego spaceships with grandchildren and walking on the beach with your attractive white-haired spouse (both of you wearing diaphanous white shirts of a vaguely Indian cut), your foot has to be amputated because, you know, diabetes.

That murderers’ row of chronic diseases (heart disease, diabetes, Alzheimer’s, etc.) might not be hard-wired into your DNA, though. Yes, a lot of late-in-life disease is part of your genetic destiny, but a study in the Archives of Internal Medicine suggests that middle-age people who do the work to stay aerobically fit will live longer, better lives.

A few details on the study: it’s a big one (nearly 19,000 participants) and a long one, starting in 1970. The fitness of participants (median age 49) was evaluated at the start, then their medical records were reviewed from 1999 through 2009.

Reynolds reminds us that even fit people die. They do live a bit longer, but “perhaps more important was the fact that they were even more likely to live well during more of their older years.”  They still get bad diseases, but they do so “significantly later in life.”

How much more quality time can you buy with a fitness regimen? “Typically, the most aerobically fit people lived with chronic illnesses in the final five years of their lives, instead of the final 10, 15 or even 20 years.”

And the best news for slugs who can process and act on this information: If you weren’t in shape until middle age, then got in shape, you did more for yourself than people who were in decent shape who made themselves into fitness beasts. So once again, beginners enjoy the biggest gains.

Photo: Ellen Jaffe Jones at Florida Senior Games, after taking gold medals for 50, 100 and 400 meters. By Ejmamawama (2012) via Wikimedia Commons.