But although they have been a couple since 2002 and have shared a home since 2004, they are not married. And among older adults, they have a lot of company.

The number of people over 50 who cohabit with an unmarried partner jumped 75 percent from 2007 to 2016, the Pew Research Center reported last month — the highest increase in any age group.

“It was a striking finding,” said Renee Stepler, a Pew research analyst. “We often think of cohabiters as being young.”

Most still are. But the number of cohabiters over age 50 rose to 4 million from 2.3 million over the decade, Ms. Stepler found, and the number over age 65 doubled to about 900,000.