Original article published on GetOld.com, brought to you by Pfizer.

When it comes to applying for Social Security or Medicare, getting a discount senior ticket at the movie theater or at a national park, your date of birth is the only relevant indication of your age.

But, in other ways, our own sense of our vitality, energy and vigor may be a more telling marker of age.

Steven Hausman, Ph.D., spent more than three decades as a biomedical researcher at the National Institutes of Health. He now lectures and consults on emerging technology, aging, nutrition and health. A vibrant 73-year-old, Hausman believes there’s strong evidence that, indeed, our subjective experience of age may be at least as relevant as what the calendar tells us.

"It's a well-known research finding that people age at different rates,"" he says. "On measures of markers like lung and heart function and the state of the immune system, the chronological age (how old you are) of an individual may not correlate with their biological age (how old you seem).""

He'll concede, however, that there are limits to the "you're only as old as your feel" concept. "There is an aging process," he says. "Certain physiological functions don't work as well with the passage of time. It takes longer to recover from injury, for one thing. At 73, I can't press 700 pounds of weight with my legs anymore."

Hausman continues with a laugh. "I can, however, still press 400 or 500 pounds."

That sly boast gets to what Hausman says is the heart of the matter. “Yes, I feel younger than I am,” he says. “But I think that’s because we all have a preconceived notion of what a particular age feels like. We may have the image of a grandparent imprinted in our memory. The reality is those images are out of date.”

That upbeat assessment is backed by a recent study conducted by researchers at Yale and the University of Southern California. Titled “Is 60 the New 50?” the investigation concluded that Americans are aging more slowly today than they were two decades ago. The reasons for this decelerated aging may be in part associated with changes in smoking, obesity and medication use.

This welcome trend may, in turn, explain why Hausman had so much fun when he recently attended his 55th high-school reunion. There was lots of lively conversation with former classmates who were very much fully engaged in life. “What being 70 was in the 1940s or 1950s is vastly different from what it is today,” he says. “I give lectures about disruptive technology, things like 3-D printing and robotics, and I can tell you, I’m having the time of my life and I have no plan on slowing down anytime soon. And lots of my contemporaries are keeping pace right beside me.”

Here are Hausman’s personal top three tips for feeling younger than your years.

1. Retire to something, not from Find new interests, pursuits, passions. “Intellectual stimulation is very important to maintaining a high quality of life,” Hausman says.
2. Follow a healthy eating plan. A good visual clue you’re on the right track: your plate is filled with vegetables in a wide variety of colors. The National Heart, Lung and Blood Institute recommends the DASH eating plan, which emphasizes a wide variety of vegetables, fruits and whole grains, along with lean protein and low-fat dairy. (The name stands for “Dietary Approaches to Stop Hypertension.) You can find detailed information, including eating plans, on the DASH page of the National Institutes of Health.
3. Make strength training a regular part of your fitness regimen. “Strength training in seniors has a wide range of benefits,” Hausman notes, “including building muscle, improving bone density and recharging metabolism.”