In February 2020, just before the pandemic began, I went skiing with my father, who was 76. This past March, my father and I returned to the trails together for the first time since then. We spent four days skiing at Snowmass in Aspen, Colo.—and from the first run, his skiing appeared different. Now 78, he seemed tentative and uncomfortable on terrain that the resort hadn’t groomed for smooth skiing. Long top-to-bottom runs—one reason East Coasters like us travel to ski out West—taxed his stamina.

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