At 74, the venture capitalist George Sarlo might not have seemed an obvious candidate for an ayahuasca experience. Mr. Sarlo's close friend, a doctor, told him about ayahuasca, a psychedelic brew made from the Banisteriopsis caapi vine, native to the Amazon. Used for centuries in sacred healing traditions throughout Central and South America, ayahuasca is now gaining popularity around the world. [It] is mostly illegal in the United States. Notably, ayahuasca's increasing popularity knows no age limits: many of those now showing interest are squarely in Mr. Sarlo's own demographic. Mr. Sarlo himself was initially skeptical. Taking ayahuasca would entail a potentially distressing night of hallucinations, and excretions of all kind, especially vomiting. But he still decided to head to Yelapa, a small village in Mexico, and swallow down the bitter brew. Mr. Sarlo said that afterward, something shifted. It changed my life completely." He realized that his life had been "absolutely full of miracles," he said. As Michael Pollan put it, "psychedelics might be wasted on the young." Mr. Pollan, the author of the recent best seller "How To Change Your Mind," a history of psychedelics and a chronicle of his own experiences trying them, said ... he was surprised by the number of people he encountered when writing his book in their 70s and 80s expressing interest in trying psychedelics. Though perhaps he shouldn't have been: as he himself has written, one of the reasons to come to psychedelics later in life is to tangle with one's own mortality.