The oddest NYC flatmate pairing is not an Oscar and a Felix, but a person 65 or older living with a much younger, unrelated roommate.

While related multi-generational households are on the upswing (high housing costs and tough economies force families to double-up) less than 1% of the NYC metro area's 6.9 million households include a person more than 65 years old living with a non-family member, according to the U.S. Census Bureau.

But the housing shortage may make more New Yorkers embrace older-younger match ups. Older residents are more likely to have purchased a great apartment or scored a cheap stabilized or controlled rental lease before prices soared. Now, as their post-retirement income sags, health flags and NYC living costs rises, roommates ease economic stress, while providing needed companionship.

And young people often find surprising benefits to living with an older, stable person who is less likely than a same-age peer to drink their Red Bull or "bring the party home," and much more likely to have nice furnishings and original art.

Easyroommate.com has seen a steady increase in the number of over 50s "choosing to cash in on their spare rooms. They now account for 11% of the total number of listings," according to Easyroommate.com spokesman Sebastiaan Ram. Women are more likely to rent an extra bedroom than men, and the average rental listed by a person over 50, is "$925 a month, a saving of $75," over the average monthly ask for an NYC share, Ram said.

Mabana Bamba, 31, says roommate Denoceta Barton, 69, is "very sharing and caring. She's kind of motherly, but she doesn't tell me what to do." Bamba, a data program assistant, found Barton through the New York Foundation for Senior Citizens' Home Sharing Program. She pays $600 a month to share the East Flatbush home of Barton, who "does most of the cooking," and often surprises her with potato salad, curries or fried chicken.

Joe DiNapoli, 69, an artist in the West Village, has opened his impressive 1,300 square-foot loft to a succession of young roommates since his wife moved out 10 years ago. ("We are reconciled -- reconciled to the fact we have more fun together when we don't live together," he explained.)

Given the escalating costs of cable, coop maintenance, groceries and NYC nightlife, having a roommate is "is not just helpful: It's mandatory," said DiNapoli, who charges $1,700 a month for his extra private bedroom and bath.

Younger, tech-savvy roomies have taught DiNapoli how to use Twitter and "navigate all the crap," on the internet.

"I like being around people," and the respectful, worldly individuals who share his home have enriched his life in numerous ways, DiNapoli said.

Living with DiNapoli for three years "worked out very well," said Francis, 38, a data analytics consultant, who just purchased an apartment of his own. As a work-oriented professional, Francis (who declined to use his last name) appreciated the "real conversations, the greater intelligence and value-added" company DiNapoli provided in addition to "a really nice place to live."

"Baby boomers are really interested in this option," because they have fond memories of sharing housing from their 20s, noted Annamarie Pluhar, author of "Sharing Housing: A Guidebook for Finding and Keeping Good Housemates." Even older people who do not have a financial incentive to open up their homes "have a social incentive: Their lives are so much better with company," said Pluhar.

"There is an overarching social need for this," affirmed Kathleen, 59, who lives rent-free with a 92-year-old woman on the LES in exchange for providing some shopping, cleaning and companionship. "I don't have full rights, exactly -- it's her house -- but there's flexibility on both our parts." Living rent-free has allowed Kathleen to "build my production business without the tremendous overhead" of New York City rent, but proscribes her from using her full name, because the apartment's owner fears irking her co-op board.

She has little to worry about, according to Michelle Maratto, a partner in Itkowitz, PLLC. Under the "roommate law," a tenant -- or shareholder -- has a right to a roommate "for reasons of economy, safety and companionship," as long as no other laws are violated. "The roommate law applies to coops, too," said Maratto. However, renters sharing their apartments can only charge half of what they are paying plus 10% under the law, Maratto said.

Adding another person to the lease, however, is complicated, far from guaranteed, and potentially costly. "You can't pick a tenant for a landlord," Maratto explained. Even if a landlord agrees to add a roommate to the lease, doing so can trigger a costly "vacancy increase" in the legal rent, said the lawyer.

Fear that her landlord will use any excuse to evict her is why M.B., 72, who has lived in her two-bedroom, two-bath rent-stabilized UES flat for 40 years, does not want her name used here. About three years ago, she began charging $1,100 a month to a succession of roommates -- medical doctors and research scientists training and working at area medical and research institutions -- but recently upped the price to $1,300 after realizing she paid the lion's share of extraneous expenses.

"There is no lease, no contracts: I just go with my gut (though she does check references) and so far I haven't had any axe murderers," said M.B. Like DiNapoli, M.B. is thrilled with her new network of "charming, wonderful friends and their families" from around the world and finds her financial stress banished.

"My friends think I'm nuts to be taking in strangers, but I really like young people -- and this is heads and shoulders better than living with a boyfriend," said M.B.