By Adam Nagourny

Los Angeles, New York Times

They lean unsteadily on canes and walkers, or roll along the sidewalks of Skid Row in beat-up wheelchairs, past soiled sleeping bags, swaying tents and piles of garbage. They wander the streets in tattered winter coats, even in the warmth of spring. They worry about the illnesses of age and how they will approach death without the help of children who long ago drifted from their lives.

“It’s hard when you get older,” said Ken Sylvas, 65, who has struggled with alcoholism and has not worked since he was fired in 2001 from a meatpacking job. “I’m in this wheelchair. I had a seizure and was in a convalescent home for two months. I just ride the bus back and forth all night.”

The homeless in America are getting old.

There were 306,000 people over 50 living on the streets in 2014, the most recent data available, a 20 percent jump since 2007, according to the Department of Housing and Urban Development. They now make up 31 percent of the nation’s homeless population.

The demographic shift is mirrored by a noticeable but not as sharp increase among homeless people ages 18 to 30, many who entered the job market during the Great Recession. They make up 24 percent of the homeless population.

Like the baby boomers, these young people came of age during an economic downturn, confronting a tight housing and job market. Many of them are former foster children or runaways, or were victims of abuse at home.

But it is the emergence of an older homeless population that is creating daunting challenges for social service agencies and governments already struggling with this crisis of poverty. “Baby boomers have health and vulnerability issues that are hard to tend to while living in the streets,” said Alice Callaghan, an Episcopal priest who has spent 35 years working with the homeless in Los Angeles.

Many older homeless people have been on the streets for almost a generation, analysts say, a legacy of the recessions of the late 1970s and early 1980s, federal housing cutbacks and an epidemic of crack cocaine. They bring with them a complicated history that may include a journey from prison to mental health clinic to rehabilitation center and back to the sidewalks.

Some are more recent arrivals and have been forced — at a time of life when some people their age are debating whether to retire to Arizona or to Florida — to learn the ways of homelessness after losing jobs in the latest economic downturn. And there are some on a fixed income who cannot afford the rent in places like Los Angeles, which has a vacancy rate of less than 3 percent.

Horace Allong, 60, said he could not afford a one-room apartment and lives in a tent on Crocker Street. Mr. Allong, who divorced his wife and left New Orleans for Los Angeles two years ago, said he lost his wallet and all of his identification two weeks after he arrived and has not been able to find a job.

“It’s the first time I’ve been on the streets, so I’m learning,” he said. “There’s nothing like Skid Row. Skid Row is another world.”

The problems with homelessness are hardly uniform across the country. The national homeless population declined by 2 percent between 2014 and 2015, according to the Department of Housing and Urban Development. Some communities — including Phoenix and Las Vegas — have declared outright victory in eliminating homelessness among veterans, a top goal of the White House.

But homelessness is rising in big cities where gentrification is on the march and housing costs are rising, like Los Angeles, New York, Honolulu and San Francisco. Los Angeles reported a 5.7 percent increase in its homeless population last year, the second year in a row it had recorded a jump. More than 20 percent of the nation’s homeless lived in California last year, according to the housing agency.

Across Southern California, the homeless live in tent encampments clustered on corners from Venice to the San Fernando Valley, and in communities sprouting under highway overpasses or in the dry bed of the Los Angeles River. Their sleeping bags and piles of belongings line sidewalks on Santa Monica Boulevard.

Along with these visible signs of homelessness come complaints about aggressive panhandling, public urination and disorderly conduct, as well as a rise in drug dealing and petty crimes.

“There is a sense out there that some communities are seeing a new visible homeless problem that they have not seen in many years,” said Dennis P. Culhane, a professor of social policy at the University of Pennsylvania.

Beleaguered officials in Los Angeles, Seattle and Hawaii have declared states of emergency, rolling out measures to combat homelessness and pledging to increase spending on low-cost housing. Honolulu has imposed a prohibition on sitting or lying on sidewalks in the neighborhood of Waikiki. San Francisco has cleared out some encampments, only for them to sprout up in other parts of the city. Seattle has tried to create designated tent camps that are overseen by social service agencies.