Age is a lot like a rubber band. It's impossible to know its limits until you try stretching it.

Lately, I've been snickering about people's conception of age. Here are two examples.The headline over a small story in the local section of one newspaper read: "Elderly man hit by car." The story went on to give the man's age as 68.Raise your hand if you think 68 is elderly.Any hand up in the air probably will belong to someone under 30. I'm sure the newspaper writer was well under 30.I can understand that when I recall my own thoughts about "old" thirty years ago. As I age, I keep changing my perceptions of "old," pushing it farther and farther away from my own age.This week I was really thinking about perceptions of age after an interview I did with an area businesswoman. She was telling me a story about an "amazing customer.""She's an elderly woman but she's not afraid to do things," said the businesswoman.I followed up with the obvious question: "How old is that amazing elderly customer?""She's almost 70," said the store owner.I couldn't help myself. I started laughing at her perception that 69 was elderly."When you're 'almost 70'," I told her, "you'll appreciate how that's a long way removed from being elderly."Now, I happen to know that businesswoman is 62. In actual years, that's not that far away from "almost 70."But in real life, it can be. Someone still involved in the rigors of working has an active life and a mind that has to function like a computer with multiple files open at the same time.When you're involved in the work-a-day world, retirement can seem like a foreign world you'll never enter. It's hard to visualize how fast the years fly by and how perceptions change as we age.A local internist who specializes in geriatrics said something interesting about age. "I'm beginning to think you can't tell anything about a person by his chronological age because there is no such thing as a typical 70-year-old," he said.He said he has some patients who shuffle slowly into his office and appear quite elderly. "When I look at their chart, I'll see it gives their age as 70. But they are in bad shape and are, indeed, elderly," he says.On the other hand, he has vibrant, active patients who look and act decades younger than the age he sees on the chart.When he said he couldn't tell anything about a patient by the age on his chart, I decided if I ever need a new internist I'll go to him.It's been my experience that too many doctors do judge us by our age.A year ago I went to an internist when my pulse rate suddenly raced too high while I was biking. I told him it was an abrupt change for me because I could always bike without having that happen.His explanation: "These things happen when we're older." He suggested I stop biking. I knew right there and then I was changing doctors because he was judging me by the age on my chart, not by my level of normal activities.Months later I learned from a heart specialist that the racing pulse rate problem happens to high school athletes as well as people of all ages. It's easily fixed and often goes away as quickly as it came.After a lot of tests that showed I have no heart problems, he concluded there was only thing I should not do: Don't sit around. He encouraged me to keep my active lifestyle.The geriatric doctor I talked with believes there is a fountain of youth that can ward off many of the negative effects of aging. It's called "exercise.""The most important advice a doctor can give you is to keep your weight down and your level of activity up," he said."We all have to get old," he added, "but we don't have to get old before our time. We can keep functioning at a high level and enjoy good health longer by staying active."The doctor talked about changes in medical thinking in the past decades. "Doctors used to tell their heart patients and those recovering from surgery to just rest. Now, we know it's far better to get patients moving right away," he says.He also tells stories about dramatic health improvements he has seen in patients. "I had one guy who had to hold onto the wall when he came in. He was in really bad shape and was on a lot of medications."The doctor told his patient two words: Get moving. "He started small and built up his endurance over time. You should see him now. He looks and feels healthy," the doctor said.Experts are telling us to get off our duffs and do some kind of exercise for at least an hour a day.If that's boring, as some say, the alternativegetting too many physical problems to be able to move - is worse.The doctor is right. People are living longer."A lot of 70-year-olds are like 40-year-olds," he says. "It all has to do with lifestyle choices."New research released this week states that those with a high level of physical activity have a 33 percent lower chance of developing Alzheimer's.Well, that's enough to convince me to stay faithful to an exercise routine. How about you?