As a youngster in East Texas, Gertha Lockett Murphy ran and waved at biplanes that soared over fields worked by sharecroppers who rarely profited from their labor.

Glenn Ratliff watched lines of people stretch several blocks to withdraw money from failed banks in Waco during the Great Depression.

In North Central San Antonio, engineer Joe Adams hammered planks and posts into a small family home during the early years of the Cold War between America and the Soviet Union.

And in the 1960s, before it was in vogue, educator Iris Meyer Sawyer gave up rich food to follow a strict dietary regimen. She was 96 when she had her first soft drink, a Diet Coke, at a McDonald's restaurant in Florida. She never tried another soda — she thought it would make her fat.

All four have something in common with a select, but growing, group of people worldwide — they have celebrated their 100th birthday. The offspring of parents born in the 1800s, they have witnessed the world evolve from horse-drawn buggies to rockets soaring in space to pocket-size computers called smartphones.

Scientists say genetics, diet, exercise, medical advances, preventive care and a little luck have led to an increase in the number of people living to 100 and older.

Experts estimate there are 450,000 centenarians now living around the world. According to the 2010 census, 53,364 centenarians were living in the United States, with 2,917 living in Texas. That's a big change from the 2,300 nationwide recorded by the first U.S. Census in 1950. The number is estimated to balloon to 6 million in 2050.

There was a time when reaching the century mark was a media event, but it's no longer a rarity. If 50 is the new 40, maybe 100 is the new 80.

As the prospect of living longer increases, concerns are growing about the quality of life of the world's fastest-growing population in terms of age.

“It's wonderful to want to live longer,” says Dr. Elizabeth Glazier, associate medical director at WellMed, “but it's even more wonderful to be extremely healthy living longer.”

Glazier says longevity could be a “double edged sword,” that could bring a significantly higher risk of Alzheimer's dementia, higher incidence of falls and people needing to walk with walkers and canes.

“For many, having longevity might mean their quality of life isn't as robust,” she says.

One reason might be a lack of specialized medical care. According to the American Geriatrics Society, there's a shortage of geriatricians — physicians who care for seniors — throughout the United States. Many people caring for older adults, general practitioners and internal medicine doctors, lack specific training in geriatrics, Glazier says.

“I think it's a nationwide problem,” she says. “What we as geriatricians can do is train internists and practitioners, the folks on the front line, in issues pertaining to geriatric patients.

An article in the May issue of National Geographic explores the genes that may be linked to longevity. Data gathered from groups of people separated by culture or locale in Calabria, Hawaii, Ecuador and New York City offer clues to gene mutations that could extend life. Genes among the group included mutations that lowered the risk of Alzheimer's disease, diabetes, cancer and heart disease.

According to the New England Centenarian Study, one in every 6,000 persons is a centenarian. Many centenarians in the study had traits in common: they rarely smoke; they are not obese; and they have relatives who lived into old age.

That last factor is true of San Antonio centenarians Murphy and Adams. Murphy's mother was 107 when she died; two aunts were 94 and 101. Adams' grandmother died at age 99, and his great-aunts lived to 101 and 102.

“Longevity is given by the Lord, it's up to him to determine how long you're going to live,” Murphy says. “He's looking down on me and blessing me.”

The 100-somethings we talked to also shared a decades-long commitment to healthy living.

Ratliff, 102, and Adams, 100, both residents at Morningside Ministries at Chandler Estate, are lean and have exercised most of their lives.

Ratliff played golf until he was 98. The game, he says, gave him an opportunity to spend time with his four sons.

“I've had a full life,” Ratliff says. “I walked every morning several blocks; never smoked, never drank. I think clean living has left me longevity.”

Adams, an engineer, worked for various branches of the military from World War II to 1960. Exercise was part of his days, either through neighborhood walks or dancing with his wife, Dorothy.

Sawyer, who is 105, has always been active, says granddaughter Tracey Sawyer-Moreno. She's particular about her health, has always eaten fish and never eats after 4 p.m.

Murphy does geriatric aerobics twice a week at the YMCA. She shops at the grocery store, cooks for herself, eats chicken, fish and many vegetables. In her spare time, she sends emails, and she has a Facebook account.

“If you settle into getting old and start shrinking back and not trying to learn things, you stop growing,” Murphy says.

Studies have shown that being sociable has helped lessen stress for centenarians.

Planning for retirements of 35 years or more could help alleviate additional worries, says Karan Bhanot, a professor in the University of Texas at San Antonio department of finance.

Retirees with extended lives would have less flexibility with their retirement accounts and need to be more conservative about spending.

“If there was an ability to set money aside in a tax-free account for medical needs during retirement, that could be very useful,” Bhanot says.

Adams has lived a life of planning and scheduling, but he says living long kind of “crept up” on him.

His fit lifestyle has helped; he doesn't need a wheelchair, walker or cane. He's a dapper dresser who could pass for a man at least 10 years younger. In fact, his age isn't really apparent until he pushes the play button on an cassette player and listens to his recorded voice speak of days long gone. To ensure his history wouldn't be lost, Adams recorded these tapes so he could pass them on to his children. As the tape turns, he gazes off, swept back to an age of silent films and Model T's.