Census statistics released Thursday reveal a portrait of a rapidly maturing Bay Area, where the proportion of children is declining and the median age is rising faster than it is statewide.
Driving the change is the baby boomer generation, which is graying the same area it transformed into a capital of youth culture in the 1960s and 1970s. California grew by 10 percent in the past decade, but there was a 60 percent growth among people in their early 60s, the fastest-growing group. The median age rose to nearly 39 in Contra Costa County, 37 in Alameda County and 45 in Marin County.
"This is the whole reason policymakers are concerned with Social Security and, to some extent, with Medicare and pensions," said demographer Hans Johnson of the Public Policy Institute of California. "We're just now getting the leading edge of the baby boomers hitting 65. In some senses, the big changes are still to come. They're occurring right now."
The shift was most dramatic in suburban hamlets such as Clayton, at the foot of Mount Diablo, where the median age rose to 45 from 40 a decade earlier.
"If you look around at the concerts, you see a fair amount of gray hair, and you see the little ones, but most of their parents are in their early 30s," said Clayton Councilwoman Julie Pierce, who moved to the Golden State from the Midwest in the early 1970s and settled in Clayton in the 1980s.
The 61-year-old is a little bit older than average in a town where about 36 percent of residents are in their 40s and 50s. People in their 40s also dominated the suburbs of Pleasanton, Danville, San Ramon and Cupertino.
The aging population is a national trend, and California is not unique.
"California seems to be aging less than some other places, which is consistent with our having a somewhat higher birthrate," said demographer Walter Schwarm, who works for the state Department of Finance. But in the Bay Area, he added, a slower growth rate and fewer children are causing the population to age more rapidly.
Demographers say the recession contributed to the aging population as the youngest adults -- many of them the children of the baby boomers -- held back on having children. Immigration slowed, and the immigrants who arrived were more likely to be older, Johnson said.
"In California, the places where you see the youngest populations are places like Imperial County and Merced County that have a lot of Latinos and a lot of young, recent arrivals," Johnson said. In the Bay Area, however, he said, "there's a larger Asian component. Asian immigrants tend to be a little older than Latino immigrants, and tend to have smaller families."
Golden Crane Senior Center, a 3-year-old nonprofit that serves mostly Chinese-American seniors living in the San Ramon Valley, offers tai chi, yoga, line-dancing and other programs to residents ages 50 to 90 at the Alamo Women's Club.
"The first year we had about 100, and then 120, and we carried that for about two years -- and then this year, all of a sudden, the population has grown from 150 last year to over 200," said board secretary Butterfly Lin. "The demand is there."
As the population of the Bay Area gets older, the changing demographics are reflected in the structure of the average family's household: In many parts of the region, fewer homes have children in them and more homes are occupied by seniors.
"When I moved into the neighborhood we had probably 300 kids just in my neighborhood, which wasn't a big subdivision. It was the young people's era of 1966," said Pinole Mayor Roy Swearingen, whose city in western Contra Costa also saw one of the highest increases in median age. The most prevalent age group in town are people in their early 50s.
The 71-year-old mayor said the culture of the town changed over the decades, and, anticipating a demographic shift, he helped drive the city to build a senior center in 1991. The building today attracts a few hundred people daily, and as the baby boomer generation prepares for seniorhood, Swearingen hopes the city can expand the site and tailor it to a more technologically savvy older population.
"A lot of those people who moved there from 1960 to 1970 are still there," he said. "We don't have a big turnaround of home sales. It stays pretty steady. There's not a lot of people moving out, not a lot of people moving in, so it gradually gets older."
The Bay Area's bigger cities, especially Oakland and San Jose, also experienced a rise in the median age at a level higher than the statewide change. San Francisco kept relatively young with its large number of late-20-somethings, but fewer people appear to be growing up there: The city was with Clayton near the bottom of the list for proportion of residents who are babies or toddlers.
And just over 3 percent of San Franciscans are between the ages of 10 and 14, compared with nearly 10 percent of the residents of suburban Diablo, Brentwood, Piedmont and Tracy.
Most of the places that aged the fastest shared a common denominator: High real estate prices and an already-settled population made it hard for younger families to move in.
"The prices rose and rose and rose and the young people couldn't afford to move there," Swearingen said. "People still can't afford to move to Pinole, unless they get a repossessed house or a foreclosure. Our high school is basically kids from out of town."
Pierce said most Clayton residents are also staying put.
"A lot of people who moved here a long time ago don't want to go anywhere else. They are staying in the homes and they love the community," she said.
In order to afford a home in the suburbs, an increasing number of families lived under the same roof as multiple relatives.
Taiwanese immigrant Yueh Tao Ju Huang, 77, was one of them. Huang said she usually enjoys the company of her adult daughter, son-in-law and four young grandchildren in a sprawling Alamo house, but she would prefer the privacy of her own home. But as a noncitizen who does not qualify for Social Security, she can't afford to live independently, she said, and so must share a home with younger generations.
Such households -- those shared with relatives other than spouses and young children -- were on the rise in many parts of the Bay Area, according to the newly released census figures. And those with young children were on the decline.
Pierce doesn't know what the future of Clayton will bring, but expects the town will age before it gets younger.
"I expect it will level off somewhat," she said. "I think there will be more younger families as the baby boomers age out and then there will be smaller booms."