If any three such disabilities persist for several weeks, he wants his health care proxy — his wife, Beth Lowd — to ensure that nobody tries to keep him alive by spoon-feeding or offering him liquids. VSED, short for “voluntarily stopping eating and drinking,” is not unheard-of as an end-of-life strategy, typically used by older adults who hope to hasten their decline from terminal conditions. But now ethicists, lawyers and older adults themselves have begun a quiet debate about whether people who develop dementia can use VSED to end their lives by including such instructions in an advance directive.

Experts know of just a handful of people with directives like Mr. Medalie’s. But dementia rates and numbers have begun a steep ascent, already afflicting an estimated 30 percent of those older than 85. Baby boomers are receiving a firsthand view of the disease’s devastation and burdens as they care for aging parents.

They may well prove receptive to the idea that they shouldn’t be kept alive if they develop dementia themselves, predicted Alan Meisel, the director of the University of Pittsburgh’s Center for Bioethics and Health Law.

“People in their 50s and 60s frequently say: ‘I don’t want to be in that situation. I don’t want to put my family in that situation,' ” he said. “And people will increasingly voice those views to others, sometimes in a formal way through advance directives.”

Mr. Medalie, fierce-eyed at 88, has seen people close to him die lingering deaths from dementia and has already decided. His motto, pithy enough for a T-shirt: “If I’m not me, I don’t want to be.”