Most opera virgins start gently, with Puccini’s “La Bohème” or “Madama Butterfly.”

Aaron Blecker’s first was Wagner’s “Tristan und Isolde” — all five hours of it. That was in 1936. Undaunted, the young accountant and his wife, Sophie, returned to the old Met opera house again and again. In 1966, when the Met decamped for Lincoln Center, the Bleckers followed.

Sophie died nine years ago, but Aaron — now 105 — is still listening. On Thursday, dapper in a herringbone jacket and Rockport shoes, he saw a dress rehearsal of the opera that started it all: “Tristan,” which opens the Met’s season Monday.

“I wish they were playing ‘Carmen,’ ” the Great Neck, LI, resident tells The Post. “Wagner was never my favorite.” But for someone who grew up poor on the Lower East Side, listening to scratchy recordings of the tenor Enrico Caruso, getting to see any opera live was a thrill, even if it meant skipping lunches and subway rides to raise the $1.10 for two tickets.

“They never missed an opera,” says his daughter-in-law, Marcia. “They were devoted to the Met.”

For the past 16 years or so, though, Blecker contented himself with catching it on the radio. But for his 99th birthday, Marcia organized a family trip to see a downtown opera company perform.

“I thought he’d be thrilled,” she says. Instead, “It’s no Met,” he told her. “Don’t bring me to this amateur stuff again.”

Other than that, his daughter Susan Cohen Rebell says he never complains. He still files tax returns (handwritten ones) for a few longtime clients and plays bridge three times a week. The only medicine he takes is baby aspirin, for his heart.

Overall, he’s an opera-loving optimist. “He just made a doctor’s appointment,” she says. “For 2017!”