Could We Live Forever? Or Even Come Close?

In a quiet Boston suburb, Esther MacKay has made it to 102 years old - and counting.

Born in 1905, MacKay traveled the world during a long career in the military. Lately she's been honored as the Air Force's longest-living chief master sergeant.

For MacKay, there's no mystery about what's gotten her this far.

"I had three no-no's in my rules growing up," she told CBS News technology correspondent Daniel Sieberg. "One was no smoking. Two was no drinking. Three, no sex. That's it, one, two, three."

Her rules may not be everyone's keys to the good life, but even if you don't follow the Esther MacKay prescription, your prognosis for living a long life is improving.

Consider how life expectancy has increased over the last two centuries. An average man born in 1800 had a life expectancy of 35 years. In 1900, he would have made it all the way to 47. By 1950, average life expectancy was up to 68 years, and now it's up to 78.

The trend is definitely favorable. But how far can we take it?

Although Ponce de Leon never found the legendary fountain of youth, today in labs like the one at the University of California, San Francisco, scientists are trying to stop the clock or at least slow it down.

In San Francisco, Professor Cynthia Kenyon is conducting experiments on microscopic worms. Their usual life span is little more than 13 days, but she has been able to get some to live as long as six times that by altering one specific gene.

"And here is the long-lived mutant when it's also 13 days old," she said, showing Sieberg her handy-work. "But you can see, look at that! It's still living a productive, active life. I would say it might be heading out to play tennis."

Kenyon believes her work shows that the rate of aging is not fixed. Rather, it can be slowed dramatically.

"The important thing for people to understand is that this is new," she said. "Fifteen years ago, and from 15 years ago on back, to when we were cavemen, cavewomen, people thought aging just happened. There's nothing you can do about it. That was it. And then along came these animals where you make a little change and they live twice as long ... Something we never thought can happen, can happen."

At the University of Wisconsin, scientists are using rhesus monkeys for similar purposes. They haven't monkeyed with their genes, but simply cut down on some of their food. For example, two monkeys are the same age, but one has eaten normally and the other is on a restricted-calorie diet and appears to have spent time at a monkey spa.

Calorie restriction research goes back more than 70 years to pioneering experiments on mice at Cornell University. Restricting your food intake does appear to extend life, although no one's totally sure how.

"If we base ideas on calorie restriction, in animals, and even in monkeys, which are relatively close to us, we see that calorie restriction slows down virtually all diseases of aging," researcher on aging at Harvard David Sinclair said.

Eat less, live longer? Easier said than done.

Brian Delaney is the president of the Calorie Restriction Society. He says it's easy to live on a calorie restricted diet, simply figure out what your normal intake of calories would be and then reduce it by 20 to 30 percent - or maybe even a bit more.

"But then you don't want to take it too far because then it's frankly starvation," he said.

Members of Delaney's group generally consume fewer than 2,000 calories a day and some go as low as 1,000 calories. Will they live longer? Is what's good for dessert-deprived monkeys also good for people?

"The CR diet could allow a human being to live to be maybe 135 or 140 years, but we don't know yet because we have not done that long a study in humans," Delaney said.

But of the course the main obstacle is: hunger. For most people, cutting calories is anything but easy.

Which is what's brought Harvard's David Sinclair to his latest project: trying to put the apparent benefits of calorie restriction - in a pill. He's now a director at a company called Sirtris Pharmaceuticals along with Dr. Christophe Westphal.

"We're not telling you 'eat whatever you want and then take our pill,'" Westphal said. "What we're saying is, 'Do the best you can on behavior, but we think we can turn on that same pathway with small molecule drugs.'"

The pill they've developed is based on a naturally-occurring substance called Resveratrol, which is found in red wine. But don't think you're going to guzzle your way to longevity: one pill has the potency of 1,000 glasses of wine.

So far the tablets are doing great things for mice. In a Sirtris video, two mice are the same age. But one mouse been taking Resveratrol and he is thriving. But it's not fair to call Resveratrol an anti-aging drug, Sinclair said.

"I sometimes slip and call it that," he said. "But actually, this is not about slowing down the aging process. It's about treating diseases that are caused by aging. And if we are successful at that, of course people will live longer, healthier lives."

The first disease they're targeting is diabetes. They hope to get Resveratrol on the market in about five years.

"Imagine a future where you're a diabetic, and your doctor prescribes you a drug," Sinclair said. "And the doctor says, 'Well, as a side effect, I have to warn you you're also protected against heart disease, cancer and Alzheimer's.' Well, you know, if we can get there, that'd be great. But that's the future that we're aiming for."

But to some people, like inventor Ray Kurzweil, a pill like that is just the first of innovations that he and others think could extend our lives for hundreds - yes hundreds - of years.

"We've gone 20,000 years without significantly changing the software that runs in our body. We have the tools now to do that," he said.

Kurzweil - you may have heard of his keyboards - foresees what he calls "the singularity," when technology and human biology merge. He's banking on the advance of technology continuing to accelerate, yielding devices like nanobots - microscopic robots that would roam your blood stream, curing what ails you.

The only problem for Kurzweil is living long enough to see it all happen. To that end, he carefully watches what he eats and takes 200 supplements throughout the day.

"You can never prove forever, because no matter how long you live, whether it's 100 or 1,000 years, that's not forever," he said. "But we can get to a point where as time goes by, you're really not aging."

But of course, mention life-spans of hundreds of years, and people usually seem to have one question: why would they want to live that long?

"Well, there's two negative thoughts that come up: One is, 'Okay, I'm gonna be a 90-year-old' as we think of them today, 'and that I'm gonna live like that for another 200 years,'" Kurzweil said. "And that's really not what we're trying to achieve. We're trying to stay in good health and really not age, so we can stay 30 or 35. We're not only going to have radical life extension, we're gonna have radical life expansion."

Dr. Thomas Perls at Boston University runs the world's largest study of centenarians. He's learned from subjects like Esther MacKay that long life isn't just a matter of genes. It has a lot to do with lifestyle.

"There is no such thing as a fountain of youth," he said. "There may be a fountain of aging well. And the fountain of aging well has to do with your good health habits, and knowing that things like smoking are truly terrible for you and can knock 20 years off your life expectancy."

And to nudge you in the right direction, Perls has developed an on-line calculator that's a bit of a crystal ball. You punch in your family history, your health and lifestyle choices, and it predicts how long you might live.

Perls, for one, is looking forward to many more healthy, happy years.

"It looks like I'll live to 94," he said. "And given what I know, that means I'm gonna be spending a big chunk of that in good health. I would love to do that."

Visit Dr. Richard Perls' Life Expectancy Calculator at www.livingto100.com.