Two days before Inez Dade was born, Woodrow Wilson was elected the 28th president of the United States. Her sister Margaret Harris came along not long after World War I broke out in Europe. Baby sister Vanilla Beane made her appearance the year Germany signed the Treaty of Versailles that ended the war, the first passenger flight took to the sky and Babe Ruth broke the home run record, with 29 in a single season.

On Saturday, the sisters gathered with relatives and friends at a 99th birthday party for Dade, whose descendants number 45 — four daughters, 13 grandchildren, 25 great-grands and three great-great-grands. The gathering at the Northwest Washington nursery school she owns also was a celebration of the lives and longevity of the sisters.

Dade and her younger sisters — Harris is 96 and Beane is 92 — attribute their longevity to hard work. They said growing up on a farm and coming of age in the Great Depression taught them the value of work, which kept their bodies strong and their minds sharp.

“I can’t believe when [young people] tell me they are tired,” she said. “How do you feel when you are tired? If I’m not hurting, I’m not tired.”

Each sister has buried her husband, lives in her own house, goes to church every Sunday and can vividly remember details of growing up in the early 1900s. Dade and Beane still work full time in their own businesses — Dade in her Tiny Tots nursery and preschool on Rock Creek Church Road NW, and Beane at Bené Millinery, the hat shop she opened on Third Street NW four decades ago.

Beane’s most famous client was Dorothy Height, longtime head of the National Council for Negro Women, who exhibited Beane’s work when she wore her hats at meetings with presidents and at other official functions. (Height herself was 98 when she died last year.)

Harris, a designer and dressmaker who dressed some of Washington’s wealthiest socialites, was sidelined a few years ago when arthritis rendered her unable to work well with the needles and thread she prefers to sewing machines. She once designed a dress working from a photograph of a Renoir painting.

Dade, who sneaked her daughters into houses she cleaned because she couldn’t afford day care, took in laundry and worked as an elevator operator until she saved enough to open her business in 1972.

“I worked three jobs at once, and nobody believed that I could,” she said. “I didn’t need much sleep. I never needed a lot of sleep because I had things to do.”

The number of older seniors is skyrocketing. In 1950, 589,612 people in the United States were 85 or older, according to the U.S. Census Bureau. By 2010, the number had grown to 5.5 million. Officials added a 90-and-over category in 2000, when 1.4 million Americans were in that age bracket. Ten years later, there were 1.8 million.

And the trend is global. The United Nations estimated that the world’s population broke the 7 billion mark last week, not so much because of the birthrate as because of people living longer.

Experts attribute the increasing longevity to improvements in health care and increased wealth, as well as changing attitudes.

“It used to be when people reached a certain age, it was, ‘Where’s the rocking chair?’ ” said Ken Budde, executive editor of AARP’s magazine. “It’s not like that anymore.”

Dade, Harris and Beane are the fourth, fifth and sixth children, respectively, of James Powell, who was born in 1877, only 12 years after slavery was abolished, and Martha Hageans Powell, who was born in 1882. James Powell was a farmer and self-taught carpenter who after a fire destroyed the family home in Wilson, N.C., built a second, with a bedroom for each of his seven children. Martha Powell did white folks’ laundry and day work in their homes.

Life was hard and money was scarce, but the Powells were a hearty, happy family, the sisters said. Each had responsibilities from the time they could walk — doing housework, taking care of younger children, tending the animals and working the fields, picking cotton and tobacco alongside the grown-ups. On Sundays, the family walked to Sandy Point Baptist Church, the girls carrying Sunday shoes to change into before entering the sanctuary.

“It was good to be on the farm,” Harris said. “We didn’t know any other way of living.”

Only Harris and Beane graduated from high school. The other children were needed to help around the place.

Dade was the first to move north, following her first husband, John Battle, when he moved to Washington in 1936 seeking better opportunities than the rural South offered blacks. She later married James Dade, a World War II veteran and federal government worker. Both men are now dead.

“I didn’t like it,” she said of life in Washington.

The couple settled into the U Street NW area, a black cultural mecca where the likes of Cab Calloway and Ella Fitzgerald played the clubs and Langston Hughes and Zora Neale Hurston regaled the black intelligentsia with their writings.

“It used to be the Broadway for blacks,” Harris said.

After two trips back to North Carolina and an admonishment from her father that she belonged with her husband, Dade settled in. In 1938, Harris joined her in the District. Beane followed in 1940.

The younger sisters loved the city.

“I got a job as a maid, housekeeping. You lived in,” Harris said. “You had a place to live, food to eat, and you got a little pay, very little pay. But you could live.”

She attended night classes to learn dressmaking and later went to work for one of the city’s prominent dressmakers. At a dance, she met Hugo Frizell Harris, a barber and minister who was her husband for 51 years. He died in 1993.

Beane married Willie Beane, a WWII veteran and butcher. They had three children, seven grandchildren and two great-grandchildren. He husband and son have since died. Like Dade, she worked as an elevator operator before taking a job with the federal government.

During the 1950s, she began to work at a hat and bridal supply shop. When the owner decided to devote his business solely to brides, Beane made her move.

“I had the opportunity, and I took it,” she said. “I had always loved making hats. It’s been a good living.”

As they look forward, the sisters have no plans to slow down. Besides hard work, they attribute their health to good genes and strong faith, although they don’t relish the attention they receive for living so long.

“What is there to write about?” Beane asked. “We are grateful to be living and doing the things we love to do. There’s nothing more to it.”

Dade had to be persuaded to agree to a story celebrating her birthday.

“You should just wait until next year and do something on my 100th,” she told a reporter.