(CNN) -- The preparation before work each morning starts in a methodical fashion. By 6 a.m., Morris Wilkinson, a 91-year-old letter carrier, irons his postal worker uniform -- a crisp, collared shirt and gray slacks -- a habit he formed while in the Marines during World War II.
He enjoys a hearty breakfast of eggs or pancakes with his wife.
He shines his black shoes.
And he's off to work.
Wilkinson, a tidy man with snow white hair and silver-framed glasses, arrives at a Birmingham, Alabama, post office promptly by 7 a.m. In his six decades working for the U.S. Postal Service, he's accumulated enough sick days to take a vacation for more than a year.
"I'd rather work than be idle," he says one morning before heading off on his route.
Forget about lackadaisical days chipping a golf ball or marking a bingo card. Workers as old as Wilkinson may be rare, but as life expectancy grows, health care advances increase and the quality of life improves, more men and women -- even in their 90s and 100s -- are choosing to forgo retirement and continue to work. Across the country, advocacy groups for older individuals such as the AARP and Experience Works are noticing workers are staying at their jobs longer and seeking new employment later in life.
"It's a combination of economics and just seeing they bring a lot of value to the workplace in terms of skills and ability," says Deborah Russell, director of workforce issues with AARP, a nonprofit agency serving Americans 50 and older.
By 2012, nearly one-fifth of the U.S. work force will be older than 55, the AARP reported. As they prepare to retire, baby boomers likely will continue to work well beyond the traditional retirement age of 65, Russell said.
One 2007 AARP study revealed that 68 percent of workers between 50 and 70 wanted to continue working in some capacity.
Choosing to work
Experts on aging say a daily job can provide older individuals with a schedule, alleviate boredom and sometimes improve their physical health. Older people also are continuing to work to supplement their retirement savings or help provide extra money for their families.
Alicia Munnell, director of the Center for Retirement Research at Boston College, says workers in their late 80s, 90s and 100s are likely working for pleasure.
"There are so few people working at those ages that it really [is] a preference," she says.
For Sally Gordon, 101, of Lincoln, Nebraska, working is a choice, but she likes the extra income, too. She uses her money to fix up her house. She's held a steady job since the late 1920s.
"I used to be a model, and now I'm a Model T," Gordon jokes. "I hope there's a lot of mileage left."
In August, Gordon was recognized by Experience Works, the nation's largest nonprofit training and employment organization for older workers, as America's Outstanding Oldest Worker for 2010. Last year's award went to a 101-year-old attorney in Texas.
The number of centenarians, people who are at least 100, has more than quadrupled in the last 30 years. The U.S. Census Bureau estimates there are 67,669 centenarians in the U.S. as of July 2010, up from 15,099 in 1980.
Gordon works for the Nebraska Legislature as a sergeant-at-arms -- a Capitol staff member who guides and maintains order. When Gordon is at work, she says she enjoys meeting new lobbyists and senators. When she isn't working, she knits blankets for charities in her community.
Age has been kind to Gordon. She has shrunk about 2 inches, but she prefers not to think about that too much. She boasts she's lost about 16 pounds, leaving her just as slender as her modeling days. She says her skin looks good for her age thanks to a routine of Clinique moisturizer and a hot washcloth rubbed on her face each night.
Gordon says she's a hard worker. She doesn't like taking breaks on the job.
"I say, 'They are paying me so I should be giving my best effort,' " she says.
Sharing life experiences
Despite stereotypes that older workers may be slower, some studies show they are more productive. They also remain at the same place of employment three times longer than a younger worker, say workplace experts at the AARP.
"There is a level of loyalty and commitment that is there. They will stay longer, and that means fewer turnovers," says Russell of the AARP.
Older workers also can provide guidance to younger workers.
"A lot of older adults have great life experience, and they like to share it," says Billy Wooten, executive director of program operations at Experience Works, which has helped 20,000 workers over 55 improve their resumes and job skills and land jobs last year.
Physically demanding careers such as construction or manufacturing are less likely to retain older workers, while industries that require a transfer of knowledge such as academics or the fields of law and medicine are more likely to have workers in their 80s, 90s and 100s, workplace experts say.
Dr. Howard W. Jones, the 99-year-old pioneer of in vitro fertilization, spent his career practicing, teaching and researching at Johns Hopkins University. He was forced to retire when he turned 65, but he wasn't ready to quit yet. He took a job at Eastern Virginia Medical School, and he has been there ever since. He already published one book this year and is working on his second.
Jones is an early bird. He begins the morning lifting light weights to strengthen his upper body, and then he heads over to his office on campus.
He is in a wheelchair and requires some assistance, but other than a weakness in his legs, he says he's in good health.
"I've been involved with this field [reproductive medicine] for more than 50 years," Jones says. "There's still much that needs to be done to make it better than it is now."
Obstacles in the workplace
Older adults still face their challenges in the workplace.
The U.S. Bureau of Labor Statistics reported the earnings of workers over 65 fell below other age groups. Median earnings for older workers in 2007 were $605 a week, lower than the median weekly earnings of $695 for all workers, the organization reported. And while older Americans may want to work, older workers have a harder time being hired, studies show.
In a contracting labor market, their chances of finding employment were reduced with budget cuts and layoffs.
So Wilkinson, the Alabama letter carrier, says he considers himself fortunate to have his job still even as the U.S. Postal Service makes service cuts and stamp hikes.
Wilkinson says his job runs smoothly except traffic occasionally will interrupt his route. He drives a white mail truck with the blue Postal Service logo. His driving record is spotless -- not a single accident.
Back in the office, Wilkinson sorts the mail, and by 9 a.m., he is ready to deliver letters and packages to more than 550 families. His favorite part is talking with families in the neighborhoods he visits. Over the years, he has attended their weddings and funerals.
At the end of the day, Wilkinson admits, he leaves the job "pretty tired."
"I may retire some day," he says. "I guess I'll retire one way or another."