What happens across your lifetime to change you from young to old is known as stochastic damage - the integrity of your bodily systems nibbled away, one damaged or misplaced clump of atoms at a time. At the detail level of molecular machinery, this is basically random. But the process is statistically predictable when you start to look at the bigger picture: our bodies are all, sadly, headed downhill in much the same general direction, and we can even talk about trends, environmental factors, and speeds of decline when we examine large groups of people.

For you, personally, what this means is that you have a ticket to ride and you can steer the bounds of the possible by your actions. But there's no such thing as absolute control - there are only risks to be shifted one way or another. Laze around and grow fat, and watch the risk of diabetes, cancer, and dementia grow much larger. Or smoke and suffer the likely consequences. Or avoid doctors like the plague for two dozen years and you're making your own bad luck, slowly but surely.

Some people sail through all that exactly because they were lucky, or both lucky and possessed of rare protective genes. Equally, you could do everything right, live the healthiest life possible, and get nailed by cancer in your twenties, or by the sudden onset of an unsuspected genetic condition in your thirties, or by an autoimmune disease despite no history of it in your family. Or, hell, by some idiot operating heavy machinery without a license while you're minding your own business on the sidewalk. These things happen. They're rare, but the point is that they're on the ticket: all you can do is swing the odds.

Some people die young and despite living well: it happens. I'm sure we can all think of a few we've known. But that doesn't remove any of the value of living well, doing the right things for your health, and generally trying to keep on the right side of heavy machinery. It's a matter of odds. Too many people look at disease in later life as exclusively bad luck, whereas they in fact had a hand in moving the needle the wrong way:

Lifetime physical inactivity interacts with secondary aging (i.e., aging caused by diseases and environmental factors) in three patterns of response. First, lifetime physical inactivity confers no apparent effects on a given set of physiological functions. Second, lifetime physical inactivity accelerates secondary aging (e.g., speeding the reduction in bone mineral density, maximal oxygen consumption, and skeletal muscle strength and power), but does not alter the primary aging of these systems. Third, a lifetime of physical activity to the age of ~60-70 years old totally prevents decrements in some age-associated risk factors for major chronic diseases, such as endothelial dysfunction and insulin resistance. The present review provides ample and compelling evidence that physical inactivity has a large impact in shortening average life expectancy. In summary, physical inactivity plays a major role in the secondary aging of many essential physiological functions, and this aging can be prevented through a lifetime of physical activity.

In some things we can make our own luck; in others we can't. Not much that can be done today about the bolt from the blue cancer in your teens, or the genetics that dealt you a heart that'll have to be nursed like the engine in a second hand car for the rest of your life. But for the rest of it: the prepared and the foresighted have what looks like great luck in life - at least from the perspective of people who didn't pay attention to all the groundwork that led to that point.

Source:
http://www.longevitymeme.org/newsletter/latest_rss_feed.cfm