When three 54-year-old viewers stood in a storefront window as passersby [guessed their ages](show/segments/view/guess-my-age-street/), answers ranged from 42 to 72 — even though all three women are 54! So why does one of the women look and feel younger than her age? "There are certain lifestyle things that put us in a position where we either feel and look older than our years or younger than our years," explains Dr. Freda Lewis-Hall, chief medical officer at Pfizer. "Genetics is an important part but it's not by any stretch of the imagination the only part," she says, pointing out that exercise and a healthy diet, for example, can slow down the aging process. Dr. Lewis-Hall adds, "How you age on the outside isn't necessarily how you age on the inside. So this is a good time for us to caution that even if you look and feel and act younger than your years, it is really important to make sure that you're on top of your health status, that you see your doctor regularly, that you have your mammogram ... Don't get complacent." Think it's too late to make a dent? Think again. "Changing your lifestyle and paying attention to your health at almost any age makes a difference," says Dr. Lewis-Hall. "It doesn't matter how old you are. If you start, you'll get the benefits. Check out Dr. Lewis-Hall's three tests that can show you how well you're aging: [balance](/show/segments/view/how-test-mdash-and-improve-mdash-your-balance/), [strength and memory](/show/segments/view/dr-fredas-tests-strength-memory/).