Adults in their 30's routinely move back in with their parents. Young artists bunk with other young artists in $3,000-a-month apartments intended for two tenants, not six. Poor immigrants wedge themselves into unsafe tenements, mimicking generations before them.

But more and more, the unforgiving math of housing economics is altering and upending the lives of older New Yorkers as well, forcing them into urgent partnerships in which embarrassment is eclipsed by necessity, fear must be swallowed and the loves and habits of a lifetime must be bent just to make do - often with complete strangers.

In Queens, Lou Tuccillo, 76, and Billy, 61, never imagined they would suddenly be bound by desperation and forced to split the rent in the way, well, college sophomores more typically might. But the deaths of Lou's wife and Billy's mother conspired to cram the two together in a cluttered apartment in Maspeth.

In the top floor of a house on Staten Island, Bob Canale, 66, and Tom Block, 62, strangers until last year, are pooling their food stamps, Social Security checks and disability benefits to stay off the streets. Yet out of their later-life crisis - Bob was assaulted and Tom's heart was weakening - they have improvised a true friendship.

Such partnerships are typically accidental, although sometimes anticipated. They can be fleeting or fixed for years. Sometimes, all it takes is a sudden slip on the stairs, and a hospitalization, draining finances and options. Sometimes, all it takes is an eviction notice from a landlord who wants to ride a hot real estate market.

"It's hard to be alone, and old, and sick, with very low income," said Irena Schafhauser, 77, who fell down the stairs of her four-story walk-up in Greenpoint, Brooklyn, a couple of years ago. Unable to continue working at a doctor's office on the Upper East Side, she reluctantly took in Eugene Swierczynski, 57, a neighbor she dislikes.

"Before, I was active, but after the accident, I can't -- " she started, fighting back sobs. "I dream a lot, to have something else, but it's very hard, because rent is life."

Capturing the doubled-up universe of aging tenants is hard because the arrangements can be short-lived, and because some are reluctant to talk about their circumstances. But according to the 2000 census, more than 9,000 households in the city consisted of people 60 and older, living with unrelated boarders or roommates.