Dec. 22, 2009 -- Feisty and determined, Ann Primack and Charlotte Eisgrou say they know the secret to longevity:
Good genes, good food, lots of milk and no alcohol.
"I mean, they can drink a little bit if they want to," Primack quickly corrected herself. "But don't overdo it."
Born prematurely at 3.5 pounds each in an east Chicago apartment in 1909, the identical twins will turn 100 years old this week.
"We lived a good life," Eisgrou told ABCNews.com from her Daytona Beach, Fla., home, where she lives independently in a condo.
"I'm here. I might as well be happy," Primack said of turning 100. "I can't go back, can I?"
They've lived through two world wars, the Great Depression and have outlived both of their husbands. They admit to a steady string of minor squabbles over the years, but spoke of decades of love, friendship and practical jokes.
"We love each other and we always will," Primack said.
Their favorite identical twin prank as adults? Switching husbands at temple to fool their fellow congregants.
"Nobody ever knew the difference. And by the time they found out, they were hysterical," Eisgrou said. "We had so much fun."
For all the similarities they share, there are some contrasts. While they both used to dye their hair red, Primack let hers grow out to a natural gray when the dye began to bother her scalp.
But Eisgrou keeps the color on.
"I didn't want to go all gray," she said. "Everybody tells me 'you look younger.'"
"They are very funny," Jerry Primack, Ann's son, told ABCNews.com. "They bicker constantly."
Primack, who lives with a caregiver in Tamarac, Fla., described herself as the flashier twin who was once a flapper in the 1920s, and liked the short dresses that were the uniform of that era. She likes fast music, she said, while Eisgrou had more classic tastes.
"Charlotte was not far behind me, but she didn't like dresses if they were too short," she told ABCNews.com.
"I was just as flashy as she was," Eisgrou shot back when she heard her sister's description of the two, pointing out that it was she who owned a car while Primack never learned to drive.
Eisgrou drove her own vehicle until a little more than a year ago when, at age 99, her son finally took away the keys, arguing that Eisgrou was too old to be behind the wheel and that the streets of Daytona Beach had gotten too dangerous for her.
"She didn't like that," Primack said. "She cried and cried and cried."
After Rough Start, Twins Live to 100
The two women do remarkably well for their age, Jerry Primack said. Though they both use a cane to walk, they are healthy and independent. Ann Primack survived ovarian cancer years ago, he added.
The twins were born Dec. 24, 1909, when their mother was seven months along. Born at home, they weighed 3.5 pounds each.
Because hospitals at the time did not have incubators or other equipment to care for such preemies, their mother's doctor put them on pillows and stuck them in the oven to keep them warm.
"He got the oven heated with a thermometer for as long as he wanted and he watched us and he took us out," Eisgrou said.
Primack said her mother knew she'd be having twins beforehand.
"She was welcoming it, but she hoped we would be all right," Primack said.
Growing up, the girls moved with their family to Chicago's West Side before they started school. They were in all the same classes, each wearing a sign with their first initial pinned on with a ribbon so their teachers and classmates would be able to tell them apart.
As they got older, they ditched the signs and Primack wore a red ribbon around her wrist. They always dressed alike in clothes their mother sewed for them.
"By 17, we minded," Eisgrou said of their matching outfits.
After graduating in 1927, they both went to work, their parents unable to afford college. Eisgrou worked as a saleslady at Sears for years while Primack did office billing for a company that made jewelry.
Eisgrou moved to Florida in 1949 with her second husband -- her high school sweetheart died after less than three years of marriage -- and the twins were forced to learn how to live apart.
Then, in 1971, Primack followed to Florida with her husband. The couples visited reguarly with their children and took long trips together.
Secret to Aging Gracefully? Milk, and Lots of It
Both of their husbands are now deceased -- Primack's husband lived to be 92 -- and while the women don't see each other as often as they'd like anymore, they talk by phone at least every other day.
"They are a trip," said Jerry Primack, who flew in from California for two of the twins' birthday parties. "They're so cute. They're just cute."
Though not as active as they once were, they both say they are staying busy. Eisgrou attends card games and excerise class in her condo building. And Primack goes out shopping with her caregiver and watches movies on television and in the theater when her son visits.
Both women say they are often asked how they managed to make it to 100.
"Everybody asks me that. I don't know what it was," Primack said. "I didn't watch my food when I was young. I smoked. We all smoked."
Eisgrou said her secret is milk, which she has drunk every single day of her life. Her sister, though, teases her for telling people that.
"I always felt that. She always laughed at me," Eisgrou said. "But it was always milk."