ARLINGTON -- The women gathered in the basement of the Fox Library one crisp evening last month, eager for the comedy and compassion that come their way during the monthly meetings of the Older First Time Moms Group.
Sitting in a circle and munching on snacks, they shared their experiences about becoming mothers for the first time after age 40. They proclaimed themselves to be the luckiest women on the planet and the oddest ducks at the playground. They fretted about saving for their children's college and their own retirement at the same time.
And they laughed about those age-exposing moments, like mentioning the singer Joan Baez to a group of new mothers and realizing nobody recognized the name.
There is no temptation here to hide age. Passing around chocolate-covered soy beans, Linda Napier, the leader of the group, who had her first child at age 43, quipped: ''Try these! You'll never get hot flashes!"
It is no coincidence that this group meets in Arlington. This town has become the epicenter of Older Mommyhood in Massachusetts, a place where one out of every 10 babies is born to a woman over 40, the most recent statistics indicate.
Once a modest bedroom community of middle-class Irish-Catholic families, Arlington has been transformed into a more affluent, cosmopolitan suburb dominated by two-income couples -- and the state's highest concentration of older mothers.
In 2003, 54 of the 560 babies born to mothers from Arlington, or nearly 10 percent, were delivered by women who had already celebrated their 40th birthday. And among these babies of older mothers, four of every 10 were born to women having their first child, according to the latest figures from the state Department of Public Health.
In Massachusetts, which has led the way nationally in delayed child-bearing, other communities such as Boston, Cambridge, Somerville, Brookline, and Newton also have a high rate of babies born to mothers 40 and older.
But the concentration of these older mothers remain highest in Arlington, a town that has become a magnet for house-hunting educated professionals who arrived late to the stroller set. For the past decade or so, Arlington has had a more plentiful stock of single-family homes at more affordable prices than other nearby suburbs, such as Lexington, Belmont, and Winchester, town officials said.
And a number of new arrivals -- many from neighboring Cambridge and Somerville -- said they were drawn to the town's hip new array of international restaurants, featuring Vietnamese, French, Indian, and Argentinian cuisine, along Arlington's bustling Massachusetts Avenue. They wanted a leafy town to raise their children that did not have a staid reputation. ''It's a child-of-the-60s demographic that just grew up and was looking for a place to live," said Jan Stetson, 55, an Arlington woman who had her two daughters at age 40 and 44.
In this town of 45,000 residents, many mothers say they have learned never to make assumptions about when -- and how -- a woman started a family.
As she left Robbins Library last month with her toddler son, Rebecca Younkin, 30, a former physics professor, recalled once seeing an older-looking woman bring a baby to the library sing-a-long. She assumed it was the baby's grandmother. ''Then she started nursing the baby," Younkin said with an embarrassed laugh. ''I was so glad I didn't say anything."
Many mothers said they knew Arlington had older first-time mothers, but had no idea it led the way. In this town, the average age at which a woman has her first child is 32 -- four years older than the statewide average and seven years older than the US average.
Despite fertility problems and health risks associated with delayed childbearing, many mothers who had their first child after 40 said they feel their older age brings many advantages: greater financial security; a wiser perspective, which allows them not to ''sweat the small stuff"; and the feeling they have experienced enough adventures to focus fully on the wonders of small children.
Still, there are jolting moments when they realize they are not like the other mothers toting babies.
Last month, a 46-year-old Arlington mother raced up to another mother to spread the word, ''Deep Throat was just revealed!" Then she realized that the mother, years younger, had the puzzled look of someone who had no idea that was the code name used in the Watergate scandal.
Such experiences can be awkward, these mothers say, but they are less so in a community where many other older mothers can empathize, and laugh, with them.
Rachel Hayes, 51, a marketing executive and mother of a 7-year-old boy, said she was at a meeting of executive women roughly her age. She found herself thinking about day care issues, while the other mothers were talking about their grown children.
Most women said they never consciously chose to delay their childbearing. Some encountered fertility problems in their 30s; others said they were too consumed with their work in their 30s to focus on children. And others simply said they did not feel ready to have a child before their 40th birthday.
Jane Huber, a book editor, said she comes from a long line of independent women who delayed having children. ''We're just late breeders," said Huber, who had her first child after she was 40.
But Sue McGovern, who had her first child at age 41 after spending years in the public-relations field, warned young women to think twice about waiting so long to have children. ''The saddest thing is that I spent so much time trudging in the land of careers when I could have magnified the wonders of being a mother," said McGovern, now 50.
Deborah Savage, 43, said she enjoyed spending her 30s pursuing her career as an international environmental consultant and does not regret waiting to start her family. Just after her 40th birthday three years ago, she gave birth to her son with the help of in vitro fertilization. This June 17, she delivered two twin girls at Beth Israel Deaconess Medical Center.
While she feels fortunate to have defied the biological clock, Savage is now preoccupied with longevity. She said she has become powerfully aware that older mothers have less time to see their children into adulthood. When she thinks of her own youngsters having babies, she imagines hoping they will hurry up. Otherwise, she acknowledged, ''I'm less likely to know my grandchildren."
Patricia Wen can be reached at email@example.com.