In particular, I recommend for your study this Periodic life table prepared by the Social Security Administration. I also have stashed a local copy because I know that it is only a matter of time before the SSA rearranges their website and this is deleted or lost.

This table will probably be a bit confusing at first, but it is worth some study. Here are some facts I have extracted from it:

• A male of age 60 is accompanied by 85 percent of the other males born when he was.
• At ae 79.5 or so, half the other males are still around -- this would seem to be the often quoted "average expected age", though in truth it is a median expected age.
• A male of age 60 is expected to live an additional 21 years (to age 81). this is an interesting statistical quirk. If you look at a subset of the people you were born with (namely those who survived with you to age 60), the expected age of that group is different and in this case greater than the whole group you were born with.

This table groups all males together - smokers, drinkers, sedentary, and so forth. It would be interested to see if there are statistics as to what effect lifestyle choices have on longevity, never mind quality of life.

Smoking is notorious for shortening human lifespan. Once source claims that if we look at two 30 year old people, the non-smoker can expect 53 more years, and the smoker can expect 35 - a difference of 18 years - pretty grim. Another source estimates that smoking shortens your life by 25 years. Some studies tabulate separate results for heavy and light smokers.

Drinking is a curious factor. Light drinkers actually live a few years longer than non drinkers, but heavy drinking shortens your life. The best advice I have read concerning this is that if you are a light drinker, keep it up. If you are a non-drinker, do not start - the risk of awakening an ugly demon is too great.

Then we come to the pretty well correlated (or anti-correlated) business of exercise and obesity. This is a big issue given that two-thirds of the American population is either overweight or obese. (One third is overweight, and one third is obese). And what is the difference between overweight and obese? An obese person is simply someone who is more overweight than you are.

Actually there are objective definitions based on "body mass index" (BMI). Your BMI is a function of your height and weight, and a quick online search will yield tables or calculators allowing you to gratify your curiosity. I am 6 foot 1 inches (73 inches) and 165 pounds, which gives me a BMI of 21.8, pretty nicely centered in "normal". For me to be "obese", I would have to weigh 230 pounds or more, in other words I would have to gain 65 pounds.
A commonly used list of categories is as follows (from the national institute of health):

• Underweight BMI less than 18.5
• Normal BMI of 18.5 - 24.9
• Overweight BMI of 25 - 29.9
• Obese BMI of 30 or greater

A lot of the articles written tip-toe around this issue (given the risk, I am sure, of offending those two thirds out there who are overweight or obese), but at least one article claims that being "seriously obese" takes as many years from your life as smoking, in other words ten or more.

On a positive note, there is a clear connection between exercise and longevity. It can add years to your life, and perhaps more importantly add years of healthy living. I have not yet found hard numbers.