Frederick Kamegni is probably eligible for insurance under the Affordable Care Act, but he didn’t know it before he walked into the Portland Community Health Center to see his doctor Monday.

Kamegni, 40, may soon join the more than 13,700 Mainers who had signed up for coverage under the federal health care law through Dec. 28.

Maine and other states had a surge in enrollment on the Affordable Care Act’s insurance marketplace last month, according to figures released Monday by the U.S. Department of Health and Human Services.

At the end of November, Maine’s enrollment was about 1,700.

Nationally, about 2.2 million had signed up for insurance by the end of 2013.

“These are very solid numbers and they show a significant demand for what’s being offered,” said U.S. Sen. Angus King of Maine. “Many who have never had coverage before now have coverage.”

In Maine, whose population is the oldest in the country, nearly half of the enrollees were in the 55-64 age bracket, the third-highest percentage in the United States. The health care law hinges on more young people buying insurance, but Maine health experts said they aren’t concerned about the large number of older enrollees in the first three months of the marketplace.

The marketplace is where individuals who don’t qualify for Medicaid – many self-employed or part-time workers – can buy subsidized insurance.

Like Kamegni, many recent immigrants don’t know that they are eligible for coverage under the law, said Libby Cummings, an outreach coordinator at the Portland Community Health Center.

Cummings has helped hundreds of people sign up for insurance, and she planned to tell Kamegni about his eligibility Monday after his appointment was completed. Kamegni, who speaks limited English, said he fled Cameroon in 2012 and is applying for political asylum.

Asylum seekers, while in the United States legally, are not permitted to work immediately and are not eligible for Medicaid.

Immigrants aren’t the only ones who don’t realize they are eligible for coverage until they are told by health center employees.

“A lot of people don’t know that they qualify for (insurance) and haven’t even thought about it yet,” said Meg Clews, a nurse practitioner at the clinic. “They’re still figuring out how the system works. I’m still figuring out how the system works.”

Leslie Brancato, executive director of the health center, said the clinic anticipates a surge in patients so it is adding two nurse practitioners to meet the demand.

“We’re experiencing much faster growth than anticipated,” Brancato said. “We have a lot of requests for new patient appointments.”

In Maine, the number of sign-ups could more than double by March 31, the end of the 2014 enrollment period, said Mitchell Stein, public policy director for Consumers for Affordable Health Care, a health advocacy group.

Stein said it’s just an educated guess at this point, but it wouldn’t be surprising to see enrollment on the marketplace reach 25,000 to 30,000 in Maine.

Wendy Wolf, president and CEO of the Maine Health Access Foundation, a nonprofit that is helping to publicize the Affordable Care Act, said the numbers are good news, especially considering the computer glitches that prevented people from signing up when the marketplace went online in October and the limited advertising for the insurance.

“I would say 13,700 is a pretty amazing figure. People are desperate to find affordable health insurance,” Wolf said.

Kevin Lewis, the head of Maine Community Health Options, one of two insurers on the marketplace in Maine, said the enrollment “exceeded expectations.” He said 80 percent of the Mainers who shop on the marketplace are choosing Maine Community Health Options’ plans.

Lewis and federal officials indicated that they are not concerned with the age mix of the enrollees because they expected many younger people to wait until closer to the March 31 deadline to enroll.

Nationally, 35 percent of those who signed up in the past three months were 55 or older. In Maine, 43 percent were 55 or older.

The health care law is intended to encourage younger, healthier people to buy coverage so that insurance premiums are reduced for older people.

“We think more and more young people are going to sign up as time goes by, which is consistent with what we’ve seen in Massachusetts,” said Gary Cohen, deputy administrator and director of the federal Center for Consumer Information and Insurance Oversight. Massachusetts started a program similar to the Affordable Care Act in the mid-2000s.

“We are actually very pleased with the percentage (of younger enrollees) that we have so far and we expect that percentage to increase,” Cohen said.

In Maine, 18 percent of the enrollees were in the 18-34 age bracket, below the national average of 25 percent.

Lewis said that although the enrollees tend to be older, it may not increase costs, because of the preventive screenings available under the Affordable Care Act and through Maine Community Health Options plans.

And Lewis said he believes that more young people will sign up.

“In the end, we’ll have a good risk pool,” he said.

Washington Bureau Chief Kevin Miller contributed to this report.

Joe Lawlor can be contacted at 791-6376 or at: jlawlor@pressherald.com Twitter: @joelawlorph