You may hear how lucky we are to live in the age of medicine, while our primitive ancestors were doomed to lifespans of only a few decades.

While it’s true that more of us are living longer — indeed, people in their 90s are one of the largest growing population groups — the idea that all people in ancient cultures lived brief lives isn’t true.

According to the Encyclopedia of Population, even though the average life expectancy for prehistoric humans was just 20 to 35 years, that doesn’t tell the whole story.

In those days, it was a victory just to survive childhood. That high childhood mortality rate skewed the statistics.

But even in ancient times, the fortunate people who managed to survive youth, disease, and accidents went on to live long, healthy lives that resembled our own.

We can learn not only from ancient cultures, but also from our neighbors around the world. Many of those countries — 19 of them, in fact — have lifespans longer than ours.

The question is: Where do people live longest? In his book The Secrets of Long Life, author Dan Buettner identified five parts of the world where the number of 100-year-olds is 10 times that of the United States.

He called these areas “blue zones” because he had circled them in blue on a map. They include:

• Okinawa, Japan. This archipelago boasts the highest prevalence of centenarians — 740 out of a population of 1.3 million have lived past  100, and they are known for their good health and vigor.

• Sardinia, Italy. Known for their long-lived farmers and shepherds, one town of 1,700 people boasts five centenarians.

• Loma Linda, Calif. A community of 9,000 Seventh Day Adventists live here, which has helped skew this town’s longevity statistics.

• Nicoya, Costa Rica. In this remote coastal town, a man who reaches the age of 60 here has twice the chance of living to 90 than in the U.S.

• Ikaria, Greece. This island has very low cancer rates, and although the people there are three times more likely to reach age 90 than Americans, there is very little dementia.

Everyone is looking for the secret of such long life. Over the decades, I’ve learned that there isn’t a single magic formula.

But I do have a set of principles anyone can use — no matter where they live — to enjoy a longer, healthier life, and beat heart disease.

I learned these principles not only from studying people around the world, but also by working with my own patients — a number of whom are over the age of 90 and living healthy, active, independent lives.