Because of longer life spans, many adult children and their parents are now “aging together,” said Kathrin Boerner, an associate professor of gerontology at the University of Massachusetts Boston.

“People in their late 60s and early 70s thought this would be a time of life when some of their responsibilities would drop off,” Dr. Boerner said. “Even though it may be a gift to still have your parents, it can be really rough.”

Besides forcing Ms. Faye to abandon her retirement dreams, her mother’s longevity has taken a financial toll. In 2001, Ms. Faye, an only child, persuaded her parents to move to Amherst from Rochester, N.Y. They paid for an addition to Ms. Faye’s home, where they intended to live. Instead, her parents moved into a three-bedroom condominium nearby. Ms. Faye and her husband, who is 77, turned the addition into a bed-and-breakfast suite. “It was fun — I loved it,” she said.

After Mrs. Meisel’s husband died five years ago, she qualified for a state program that paid some of the costs of home aides. While Ms. Faye ran her B&B, she paid for round-the-clock care for Mrs. Meisel and her mother’s other expenses by dipping into a nest egg of about $250,000 that her father left. Within several years, the money was gone, she said.

On the advice of a financial adviser, Ms. Faye has put her house — with her “fabulous” gardens and an art studio — on the market. The B&B is closed. Ms. Faye and her husband moved into Mrs. Meisel’s condo, and her mother moved into a one-bedroom unit in the same building.