SACRAMENTO, Calif. -- The ceremony in February seemed like a traditional celebration. One of Charlotte Benedict's sons walked her down the aisle in the Eskaton Village Carmichael auditorium, while two of Jim Jordan's sons stood up with him. A minister blessed their union.

"We had 150 people there," said Jordan, 85, a retired architect and engineer. "But we didn't have a wedding license."

It's a quiet little fact of senior residences across the country: Grandpa is living with someone else's Grandma.

In their 70s, 80s and beyond, older couples meet in seniors-only housing and live together unencumbered by marriage vows. Their relationships are committed and bonded, meant to last the rest of their lives, sometimes even informally blessed by clergy.

According to U.S. census figures, co-habitation numbers for people 65 and older have tripled in the past decade. A generation or two ago, the idea of older adults living together might have been shameful, even scandalous. That's changed, in part because societal attitudes toward marriage have changed.

Only 52 percent of American adults identified themselves as married in the 2010 census, and almost 60 percent of people age 50 and younger have lived with a partner without being married, the Pew Research Center says.

As a result, as the baby-boom generation edges into old age, researchers expect co-habitation among seniors to continue to soar.

Beyond the lifting of societal taboos against co-habitation, experts agree that there's one key reason that older people live together instead of tying the knot: money.

A widow who receives her late husband's Social Security and pension will forfeit that income if she remarries, said Susan Brown, a Bowling Green State University sociology professor who has studied older age co-habitation. While this is true for those under age 60 (50 for the disabled), those aged 60 or older will still qualify for benefits.

And older adults often don't want to complicate terms of their wills by bringing new spouses into the family picture, said Johns Hopkins sociologist Andrew Cherlin. "So they think, 'Let's be a couple but not disrupt the benefits we get or promises we made to our children,' " he said. "I don't think it's a cultural statement. I think it's a statement about economics and inheritance."

Late-life co-habitation also is about love and the life-affirming decision to move beyond a lifetime of losses.

"As we get older, we go through tremendous losses," said Fair Oaks marriage and family therapist Helene Van Sant-Klein. "We lose parents and spouses and friends.

"Establishing an intimate relationship in older age presents another opportunity to gain connection and feel that sense of significance and belonging."