An estimated 73,674 Americans were 100 or older in 2004, according to the U.S. Census Bureau. That's the most recent year the agency has estimated the number of centenarians. And that's a whole lot more than there used to be – and whole lot fewer than there are likely to be. There were about 3,000 centenarians in the U.S. in 1950, and 37,306 in 1990, according to the Census Bureau. It estimates that in 2050 there will be 1.1 million. Live right, and you might be one. Although many people think longevity is all about the genes, it's really one-quarter about the genes and three-quarters about lifestyle, says Steven Austad, one of the country's foremost experts on aging and author of the book Why We Age (Wiley, $16.95).  He believes the person is alive today who will be the first human to live to 150. The record so far is Jeanne Calment of France, a wealthy woman who never had to work. She died in 1997 at 122 years, 5 months and 14 days. Her advice? "Always keep your smile." Read on for tips on how to live to 100, including some from those already at the party.

1) Be positive. Cheerful, optimistic people decrease their risk of early death and poor health by 50 percent over sourpusses, according to researchers at the Mayo Clinic.

2) Learn to manage your stress. Stress can damage your health, from your heart to your digestive system. Figure out the best way to manage it, be it exercise, yoga, meditation or eliminating the causes of stress.

3) Learn to say no. If you don't want to do it, if it's going to stress you out, then just say no. You can't do everything, and you can't always make everyone happy. Look out for No. 1 (without being a jerk, of course).

4) Dance, sing. Find something that makes you feel euphoric, and then do it, and keep on doing it. Dancing is great exercise, too.

5) Find passion for the little things in life. Love for the theater or gardening or art or reading keeps the mind active and can give you joy and a sense of purpose in life.

6) Be smart about what – and how much – you eat. We'll keep saying it until you die. Eat more fruits and vegetables and less red meat and fries. And when you're full, stop eating.

7) Exercise. If you can't manage 30 minutes a day of aerobic exercise, then do what you can. Just start, then work to make it regular.

8) Exercise your brain. It needs exercise just as your body does. Solve puzzles, take classes, play chess or bridge, learn to play an instrument. Retain your curiosity. Never stop learning.

9) Stay active. Get out of that chair and off the couch. Go for a walk, go to the mall. Work in the garden, mow your lawn.

10) Stay connected. Maintain a network of friends. Be friendly with your neighbors. Isolation leads to depression.

11) Read a newspaper. This may seem self-serving, coming from us, but there's no better, easier way of finding out what's going on, of staying interested and involved, than the newspaper.

12) Quit smoking. Just stop. Please.

13) Drink in moderation. Studies have shown that a glass of red wine or ale every day reduces the risk of cardiovascular disease.

14) Get, or stay thin. Researchers ave extended the lives of laboratory animals by drastically reducing calorie intact. They say that thinner is better if you want to live to 100.

15) Limit exposure to the sun. The sun will not only wrinkle your skin, but it also can cause skin cancer, and that can kill you.

16) Find a good doctor and get regular checkups. Preventive medicine is your best bet for catching potential fatal diseases in their early, and treatable, stages.

17) Keep track of your medications – and take them. If you're having trouble keeping them straight, then let someone help you.

18) Control blood pressure early because as you age, your vascular health can worsen. Controlling hypertension helps slow the aging of your blood vessels.

19) Don't be complacent about high-normal blood pressure because that's increasingly seen as pre-hypertension. Your risk of developing hypertension increases with a blood pressure higher than 115 over 75. Anything you can do to reduce your risk of hypertension can add years to your life.

20) Keep the medications simple. The more medications you add, the more it costs, the more side effects may increase and the more complex it will be to keep track of them. There are more than 100 medications to treat hypertension, but the average number of medications needed for any one patient is 3.5.

21) Don't let mental illness go untreated. Depression and other psychological conditions can contribute to poor quality of life, and may compromise the body's ability to recover from injury and illness.

22) Establish healthy habits early in life. Exercise and eat a balanced diet when you're young. Overweight children most often become overweight adults – and that carries with it a host of risk factors for heart disease, diabetes and other serious medical conditions.

23) Get your blood pressure and cholesterol checked regularly. They're treatable risk factors for cardiovascular disease, which causes heart attacks, strokes and other deadly conditions. The tests are quick and easy, and medical treatments are effective.

24) Don't ride motorcycles. This actually doesn't affect heart health, but he's noticed over the years that motorcycles send a lot of patients to the emergency room.

25) Take to the water. The best exercise for the elderly is water aerobics because it is an exercise that does not put a burden on weight-bearing joints such as the knees.

26) Dump the dead wood. Hang out with cheerful people; grouches bring you down.

27) Cultivate a support system. Whether it's that gentle nagging by your partner to get your annual physical or it's a concerned friend reminding you to take your blood-pressure medicine, the benefits of a support system are numerous.

28) Get a pet. Pets keep you smiling and can keep you active. They're good company, too. But don't forgo the human contact.

29) Learn how to use a computer. Web sites such as AARP's ( www.aarp.org) are loaded with information about health, fitness, money and food. Just don't sit too long in front of the computer.

30) Remember: It's never too late. No matter how old you are, you can benefit from a healthier lifestyle.

SOURCES: AARP; www.about.com; www.msnbc.msn.com; Dr. John A. Collins; Dr. Jeffrey Ross., Dr. Mitch Carroll, Dr. Bassem Elsawy, Dr. Jeremy Denning, Dr. Jack W. Spitzberg