Society is in persistent denial of some important truths about aging. We view the aged as sick, demented, frail, weak, disabled, powerless, sexless, passive, alone, unhappy and unable to learn -- in short, a rapidly growing mass of irreversibly ill, irretrievable older Americans. To make use of new scientific knowledge and to experience its benefits, we must "unlearn" the myths of aging.

Myth: To be old is to be sick.

Fact: The theory that older people become sicker and more dependent with increasing age is losing favor. MacArthur studies and other research show that older people are much more likely to age well than to become decrepit and dependent. Only 5.2 percent of older people reside in nursing homes, down from 6.3 percent in 1982.

Furthermore, most older Americans are free of disabilities. Of those Americans aged 65 to 74 in 1994, a full 89 percent reported no disability whatsoever. While the proportion of elderly who are fully functioning and robust declines with advancing age, between the ages of 75 and 84, 73 percent reported no disability. Even after age 85, 40 percent were fully functional.

The reduction in disability appears to be accelerating. This is true at all ages, even among those over age 95.

Myth: You can't teach an old dog new tricks.

Fact: The pervasive belief among young and old that the elderly cannot sharpen or broaden their minds creates a disturbing cycle of mental inactivity and decay. Certainly, the less people are challenged, the less they can perform. But research shows that older people can, and do, learn new things -- and learn them well.

True, the limits of learning, and especially the pace of learning, are more restricted in age than in youth. And the conditions for successful learning are different for older people than for the young.

Three key features predict strong mental function in old age: regular physical activity; a strong social support system; and belief in one's ability to handle what life has to offer. Happily, all three can be initiated or increased, even later in life.

Research has demonstrated the remarkable and enduring capacity of the aged brain to make new connections, absorb new information and thus acquire new skills. In one experiment, older people who showed declines in inductive reasoning and spatial orientation made significant and long-lasting improvement after five training sessions.

Myth: The horse is out of the barn.

Fact: Many believe that, after decades of fat-laden foods, no exercise and overindulging in alcohol, what they have lost is gone forever and cannot be recovered. But nature is remarkably forgiving. Research shows that it is almost never too late to begin healthy habits such as smoking cessation, sensible diet and exercise. And it's never too late to benefit from those changes.

The risk of heart disease begins to fall almost as soon as you quit smoking -- no matter how long you've smoked. In five years, an ex-smoker is not much more likely to have heart disease than someone who never smoked -- and the good effects of quitting hold regardless of age, how much or how long you smoked.

Similar results can also come from changes in obesity, blood sugar, blood pressure, cholesterol, triglycerides and exercise.

Myth: The secret to successful aging is to choose your parents wisely.

Fact: While the role of genetics in aging is important, it has been tremendously overstated. A common error is to assume that one's genetic predisposition is equivalent to genetic "control" of life expectancy, and that we are all preprogrammed for a given duration of life.

With rare exceptions, only about 30 percent of physical aging can be blamed on genes and only about half of changes in mental function. This leaves substantial room for healthy lifestyle to protect the mind and body. Also, as we grow older, genetics becomes less important and environmental factors more important.

The likelihood of being fat and of having hypertension and high cholesterol, and the rate at which one's lung function declines with advancing age are, by and large, not inherited. These risks are due to environmental or lifestyle factors. How we live and where we live have the most profound impact on age-related changes in the function of many organs throughout the body.

Myth: The lights may be on, but the voltage is low.

Fact: This myth suggests that older people suffer from inadequate physical and mental abilities. Sexual activity does tend to decrease in old age. However, there are tremendous individual differences in this intimate aspect of life. We know that these differences are determined in part by cultural norms, by health or illness, and by the availability of sexual and romantic partners. When it comes to sexual activity, as in so many other aspects of aging, chronological age itself is not the critical factor.

Certainly there are older people who have lost interest in sex and are glad to be done with it. But that is not the dominant view of older men and women in the United States today. One study found that about 70 percent of 68-year-old men were sexually active on a regular basis. At age 78, this dropped to about 25 percent, due mostly to health. Among older women, the major factor for declining sexual activity was the unavailability of an appropriate partner.

Apart from sexual activity, the basic human need for affectionate physical contact, which is apparent even in newborn infants, persists throughout life. The voltage is never too low for that -- in fact, it may help keep the lights on.

Myth: The elderly don't pull their own weight.

Fact: The unstated assumptions are that everybody who works for pay is pulling his or her weight and that those who do not are a burden. The truth is, some people who are paid do little or nothing useful while unpaid but productive work -- in the home or as a volunteer -- is uncounted.

As people age, and especially as they retire from paid work, their continuing productive activities are increasingly unpaid. One-third of older Americans work for pay and one-third work as volunteers in churches, hospitals and other organizations. Others provide informal, much-needed assistance to family members, friends and neighbors. It would take 3 million paid caregivers, working full time, to provide that assistance to sick and disabled people.

Also, for many people retirement, while not legally compelled, is nevertheless involuntary. Many employers seem to believe, mistakenly, that older workers are less productive, more often absent or are liabilities in some other respect. Millions of seniors are ready, willing and able to increase their productivity, both paid and voluntary, given a chance.

John W. Rowe is a physician and the president of the Mount Sinai School of Medicine and Mount Sinai Hospital in New York. Robert L. Kahn is professor emeritus of psychology and public health at the University of Michigan. This article is excerpted from their book "Successful Aging" (Pantheon 1998).