Broadway isn’t just for old fogeys.

Case in point: The new Broadway tuner “13,” which features an all-teen cast and orchestra. The show marks the Rialto debut for almost all of its performers.

The production is the brainchild of Jason Robert Brown, the composer-lyricist (“The Last Five Years,” “Urban Cowboy”) who picked up a 1999 Tony for his score for “Parade.”

He was originally approached a few years ago to create a young-adult book that would have a companion musical. That particular version of the project never came together, but eventually Brown’s idea morphed into the musical opening Sunday on Broadway, after a run at the Mark Taper Forum in Los Angeles two seasons ago and a stint at Goodspeed Musicals earlier this year. (Coming full circle, a related YA novel — “13: A Novel” — was recently released, penned by Brown and Dan Elish, who co-writes the book of the tuner with Robert Horn.)

Though the show, about a young New Yorker who finds himself uprooted to Indiana, was originally Brown’s creation, don’t look for any real-life tidbits from his youth.

“Autobiographically, I’m nowhere near this,” he says. “But emotionally, I’m all over it.”

He writes squarely in a rock idiom, a far cry from, for instance, the more traditional tuner mode of “Parade.” “I’m writing for character,” he explains. “A bunch of 13-year-olds in contemporary America will sound like contemporary music.”

According to him, the process of finding the show’s cast of “astonishingly talented” teens was tough, in large part because often even gifted young performers haven’t yet cultivated strong audition skills.

He adds, though, that he’s learned as much from his young cast as they have from him.

“I have to open myself to these kids and give them all this love and joy and room to explore,” he says. “And the kids give that back to me so much.”

Recent breakthrough: The Tony winner’s kidcentric musical “13” opens on Broadway Sunday.

 Role model: “Thornton Wilder, in terms of his ability as a writer to continue exploring. He never repeated himself.”

 What’s next: “The Trumpet of the Swan,” an adaptation of the E.B. White book, bows at the Kennedy Center in December.