When you’re 53, as I am, and believe yourself to be on the wrong side of life’s unknowable midpoint, a conversation with someone who will soon be twice your age, and who furthermore has retained all his marbles, can be disorienting. For one thing, it has the effect of collapsing a century into a pancake. Czar Nicholas II and Barack Obama, gaslight and computer glow, grandmothers and grandchildren: All are contemporaries, all in sharp focus.