(CNN) -- Still vigorous at 100 years of age, Edward Rondthaler writes a weekly column for his local newspaper, walks a half-mile every morning and drives himself on errands around his hometown of Croton-on-Hudson, New York.
Rondthaler credits his long and healthy life to clean living, good genes, and regular cold showers.
"When my brother in 1918 came home from the army, he said, 'Ed, whenever you take a hot shower, end it with an ice cold one and count to 100.' When your older brother tells you to do something, you do it," Rondthaler said.
Ever since, Rondthaler has finished his morning shower with a long blast of cold water, which he thinks plays at least a small role in keeping him going.
"I've learned to count pretty fast. It gets you out of the tub quickly," he said.
Rondthaler is a member of what demographers say is the fastest-growing segment of society -- centenarians, or people 100 years old and above. He and his cohort are increasing in number because more Americans are living longer than previous generations.
Reduced mortality
Over the past century, life expectancy in the United States has increased about 30 years, according to the Centers for Disease Control and Prevention. This has brought the average life expectancy from 47.3 years for someone born in 1900 to 77.3 years for someone born in 2002.
"It comes to largely drops in infant mortality that took place over decades. Also improvements in public health, vaccines, ways to prevent killer diseases, keeping the water supply clean," said Winifred K. Rossi, deputy associate director of the Geriatrics and Clinical Gerontology Program at the National Institute on Aging.
The increase in longevity has been larger for women than men. Two years separated their average life spans at the turn of the last century. Now, more than 100 years later, five years separate the sexes, with the average man living 74.5 years and the average woman living 79.9 years, according to the CDC.
"Women are not as prone to having acute events such as fatal cardiovascular problems or other quicker killers. Males are at more risk. A lot of it is driven by lifestyle and environment. Men tend to engage in riskier behaviors, such as smoking," Rossi said.
Centenarian secrets
Demographers and public health experts are split over whether the next century will see longevity increases like the last one.
Some experts believe life span growth will slow because infant mortality, the major cause of shorter life spans in the past, largely has been wiped-out. Other experts counter that advances in genetic technology will enable people to live significantly longer lives.
Regardless, there are some concrete steps people can take to maximize their own life span.
Thomas Perls, director of the New England Centenarian Study, examines people age 100 and above in order to help everyone else learn how to age well.
He says the key to a long and healthy life is rather simple: Don't smoke, gets lots of exercise and sleep, and eat a balanced diet.
"One of the important messages here is that it doesn't have to be unusual. It is what your mother told you to do, with the exception of clearing your plate," Perls said.
Centenarians are a diverse group, according to Perls. Some are teetotalers. Others manage to reach extreme old age despite heavy drinking and smoking, deadly behaviors for most people. One feature common to most centenarians is that stress doesn't bother them.
"They seem to be able to shed stress. It doesn't get to them and cause them to age more quickly. They don't internalize stuff," Perls said.
Rethinking retirement
As more and more people live longer, many of them are rethinking what it means to be old.
Dan Kadlec, co-author of "The Power Years: A User's Guide to the Rest of Your Life," says baby boomers will revolutionize retirement, which the first wave of them will enter in just a few years.
"I'm a boomer myself. I've watched, and many of us have watched, our parents retire way too early thinking they weren't going to live much longer. They wanted to get their wills in order and play golf and pinochle," Kadlec said.
As a result, Kadlec thinks his generation will be more interested in exploring second and third careers, traveling widely and perhaps even having more sex.
"The obvious example is Viagra. It has changed a lot of men's lives, even in their 70s and 80s. There are medical breakthroughs all the time that are extending life and the quality of life. That is what is behind the longevity revolution. It's not just that we are living longer. It is that we are living longer and better," Kadlec said.
Rondthaler, the 100-year-old from Croton-on-Hudson, says community involvement has helped him live a long and full life.
Rondthaler likes to sing, and is writing a song for the 100-year anniversary of the Croton Dam, which holds drinking water for New York City.
"As you can imagine, a 100-year-old is always invited to things," Rondthaler said. "I'm always working up ballads for any event, like the 100-year anniversary of the dam."
Rondthaler is even healthy enough to give blood, which he plans to do soon.
"The doctor gave me permission to give blood. They want to make a point of it. They want to say, 'Here's a 100-year-old man giving blood. Why don't you young people try it too?'"