The Quest to Slow or Stop the Aging Process Re "When I'm Sixty-Four," by Roger Cohen (column, Dec. 25): We do not need Internet billionaires such as Larry Page or Peter Thiel to find ways to extend people's lives to 120 and beyond. It is the thousands of researchers working to conquer cancer, diabetes, heart disease and Alzheimer's who are going to allow a large percentage of those alive today to live well beyond 100. Would Mr. Cohen rather have these scientists stop their research and let people die at what he feels is the proper age of 85 or 90? While a majority of Americans surveyed may say that their ideal life span would be to live to 90, what would be the response of those who are already 90 or older (there are about two million such Americans) and of sound mind and body? Would any of them say they've lived long enough and are ready to die to make room for others? The writer is a professor of clinical neurology at SUNY Downstate Medical Center and director of the New York Headache Center. Roger Cohen worries that a radical extension of human health, as now sought by members of the medical research community like me and by several dot.com gurus, would make his life terminally dull, "a featureless expanse," as he puts it. Even accepting that attitude, a more frightening prospect than looking ahead to an endless, featureless expanse might be looking ahead to a life of wheelchair-bound demented mental vacancy. That fate awaits many of us who reach 85, unless science indeed finds a way to extend health. The writer is a researcher at the Barshop Institute for Longevity and Aging Studies, University of Texas Health Science Center.