If you want to live long and well, get ready now. Health experts say it's time to shift the goal from just living as long as possible to staying healthy longer.

"You want to lengthen the number of healthy years," said physician Edward Schneider, Dean of the Leonard Davis School of Gerontology at the University of Southern California. But keeping healthy into old age doesn't just happen for most people--it requires decades of planning.

"You must start preparing to be in tiptop shape," said physician George Blackburn, Associate Director of the division of nutrition at Harvard Medical School. According to the National Center for Health Statistics, a person who makes it to age 65 will live, on average, 17.9 more years. "Now it's just a matter of what quality of life that will be," Blackburn said. "Who wants to live 17 years in a chronic disease state because you frittered away your 40s and 50s?"

Keeping your body functioning into old age can mean the difference between going to the bathroom on your own or needing help, or the difference between playing with the grandkids or just watching them. "Do you want to be sitting in front of the TV or be out on the golf course having a good time?" said Schneider, who took part in the MacArthur Foundation Study of Successful Aging and has written a new book, AgeLess.

So how best to hang on to what you've got? Certain aspects of aging are unavoidable. For example, there's almost no getting around reading glasses. "The magic age for that is like 45," said Charles Nichols, Deputy Chief of Ophthalmology at the University of Pennsylvania. Also, brain changes mean you're likely to start experiencing so-called senior moments, usually lapses in recalling a name or word. "People notice it in their 40s," said Guila Glosser, a Penn neuropsychologist. "You have difficulty finding words and names. You know what you ought to say and you can't get it out...It's bothersome, but the reality is there is nothing you can do about it. You wait and it comes back to you."

But other things, such as decline in bone and muscle mass that comes with aging, and the onset of conditions such as high blood pressure, diabetes, high cholesterol and heart disease, can often be slowed or averted altogether. "Many of the chronic diseases of old age are best prevented by healthy living starting in early middle age and before," said Stanley Slater, Deputy Associate Director of geriatrics and clinical gerontology at the National Institute on Aging.

Last month two British researchers made a provocative proposal that everyone over age 55 pop a daily "polypill"--a for-now-theoretical concoction of aspirin, a cholesterol drug, three blood pressure medications, and folic acid--with the aim of cutting the incidence of heart disease and stroke by at least 80 percent.

Other experts offer advice that is more prosaic than a magic pill: Don't smoke, keep the weight off, exercise nearly every day, doing both aerobic and strength-building activities, and load up on fruits and vegetables. "We really want to intervene and prevent disease. We like to work on things before they develop," said Deborah Witt, a family physician at Thomas Jefferson University Hospital.

Diabetes, for instance, can be a devastating disease, ravaging everything from the eyes and kidneys to the feet, and leading to permanent disabilities such as blindness and amputations. Yet even a modest weight loss and regular exercise can help prevent it. High blood pressure, a leading cause of heart disease and stroke, also can be controlled by losing weight and exercising.

Slater said that while bad habits were usually well-ingrained by middle age and changing them could be tough, "start today, and if today is fairly late, it's still better late than never." He said the ultimate objective was to "live well and then get sick and die very quickly." "You stay strong and vigorous, avoid frailty, and suddenly, boom, you die," he said.