FLORHAM PARK, N.J. — Shortly after the New York Jets chose a quarterback out of the University of Southern California with the third overall pick in April’s NFL draft, the team’s incumbent at the position, Josh McCown, received a text from his oldest daughter, Bridget.

“He’s less than a year older than me,” she said. “Crazy.”

The 39-year-old McCown could only chuckle. He would still fight to earn the starting job for the Jets for a second straight season, but this year, he would lose that battle.

The Jets’ brain trust has decided it simply cannot wait to anoint its most promising quarterback prospect in 50 years. On Monday, at 21 years 97 days old, Sam Darnold will become the youngest quarterback to start an NFL season opener since 1970, and the second-youngest quarterback ever to start a game. Only Tommy Maddox, who filled in for the injured John Elway of the Denver Broncos in Week 11 of the 1992 season, started at a younger age (21 years 81 days).

This, of course, is a different time, a different city, a different, more desperate franchise. The Jets have drafted four other quarterbacks in the first round since Joe Namath in 1965. It has not gone well. None could ultimately match what Namath did once: win a Super Bowl.

With Darnold, there is a buzz that eclipses even the hype around Mark Sanchez, another USC product, who started as a rookie nine years ago and took the Jets to two consecutive AFC Championship games before his Jets career skidded downhill toward a notorious “butt fumble” and ended with a mediocre 33-29 record.

Sanchez was often considered immature, someone who embraced the playboy lifestyle and the trappings of a big-market football star; Darnold is a self-described introvert. He went back to his hotel room and ordered pizzas the night he was drafted.

Darnold’s father used to call him Flatline, for his stoicism.

“He doesn’t act like a 21-year-old,” said his former USC center, Nico Falah, now a practice squad teammate with the Jets. “He acts three or four years older than his age.”

Yet, Darnold is something else, too — a true 21st-century product of the left coast, who brings plenty of the New Age accouterments that can accompany a certain style of elite athlete raised in that part of the world these days. Darnold has embraced yoga and guided meditation, through the Headspace app, as a twice-daily routine for channeling focus. He co-hosted a podcast to get out of his comfort zone and overcome his shyness.

His desire to fortify the mental side of his performance has helped foster a special relationship with a prominent sports psychologist, Michael Gervais, who has worked for the Seattle Seahawks for eight seasons and is known for his attention to mindfulness and for bringing an athlete’s deepest fears to the surface. Gervais considers Darnold to be exceptionally cerebral, which is all well and good, except Jets fans — not known for gushing patience and tolerance — really just need him to hit the receiver over the middle on a post pattern.

Will Darnold’s mindfulness help that cause? Given the scenario that Darnold is about to step into, Gervais said, the quarterback’s mental makeup will be just as critical as his physical gifts.

“He’s got a unique situation,” Gervais said. “He’s a rookie starting in one of the most intense professional environments — New York — with a group of alpha competitors.”

But, Gervais added: “Sam’s orientation is to be a learner, to grow, to figure things out. That’s going to create a lot of space for him to be able to work on his craft. I don’t think Sam’s going to get caught up in as much noise as people are afraid he might get caught in. The best athletes in the world understand that mastery of what’s in their control is a requirement.”

Darnold’s rise to stardom was swift. As a sophomore at San Clemente High School in California in 2012, he played wide receiver and linebacker. He was so widely overlooked as a junior that his coach, Jaime Ortiz, sent basketball highlight tapes to football recruiters to showcase his athleticism. At the Elite 11 camp, a competition to name the nation’s top 11 high school quarterbacks, Darnold came in at No. 12.

But he has proved remarkably quick on the uptake. As a redshirt freshman at USC, he used to torch the scout team, Falah said. Now he has a lightning arm that can be freakishly accurate. He is not likely to turn heads with a fiery speech or locker-room outburst, something his former teammates said was never his style. They rallied around his actions.

Darnold still sports the board shorts and Vans sneakers that formed his off-field “uniform” as a Southern California surfer dude, though he does not surf. He also wears a red wristband in honor of his friend, Nick Pasquale, who was struck by a car and killed while the two were in high school.

“Leadership is actually more akin to consistency of authenticity across stressful environments,” Gervais said. In other words, “we trust people when we know how they’re going to show up.”

Darnold has not given any indication that his internal temperature has changed since the Jets traded up to draft him in April.

“I’m sure he’s got highs and lows,” said Todd Bowles, the Jets’ stoic coach. “He hides it probably as well as I do right now.”

After practice recently, Darnold said he understood the expectations for the top pick of a franchise seven years removed from its last playoff experience, and he has cultivated a support group to manage them.

“I have really good friends, really good family, really good guys in this locker room that I can lean on whenever things happen or whether it’s bad or whether it’s good,” he said.

He is not immune to nerves. Last fall, he co-hosted a podcast each week with Yogi Roth, a former college wide receiver and now an analyst for the Pac-12 Network. But it was Darnold who was asked to lead the show, which featured guests like former NHL star Luc Robitaille and actor Will Ferrell.

It was an unusual arrangement for a college athlete. Darnold, on the first episode, said that he was shy growing up and still not entirely comfortable in front of a microphone.

“I think I’m a better listener than I am a talker,” he said on the show. He and Roth met every Monday night for a production meeting. They recorded the next day, in the basement of Heritage Hall.

“I told him you’ve got to treat it like it’s one of your most important courses,” Roth said. “He leaned right in.”

The goal, of course, was to put Darnold more at ease being in the spotlight, handling the news media and thinking quickly on his feet in other ways beyond the football field. Darnold, Roth said, possessed the trait that he thinks is the most undervalued in quarterbacks: a desire to “seek” information.

“A lot of the elite athletes are thinkers,” Roth said. “I truly think the essence of the craft is one that is an artistic mind. And a lot of times, the creative minds are quieter. It doesn’t mean that they’re soft or they’re weak. It’s actually the opposite.”

Among the podcast guests was Gervais, whom Darnold first met when the psychologist spoke at the Elite 11 camp in 2014. Darnold, the Californian, soaked up Gervais’ message about establishing the right psychological frameworks to command his inner, mental experience. The two have remained in touch.

“He’s curious, he has a deep commitment to learning, and he’s just got a way about himself where his character strengths flourish in both calm environments and hostile environments,” Gervais said.

There may be plenty of hostile environments ahead. The Jets were 5-11 the past two seasons, and while some NFL rookie quarterbacks have had successes in recent years (Matt Ryan in 2008, Robert Griffin III in 2012, Dak Prescott in 2016), great quarterbacks such as Terry Bradshaw, John Elway, Troy Aikman and Peyton Manning struggled initially after starting Week 1.

The Jets, though are ready to embrace the future. “Our guy came in and learned everything,” Bowles said. “And he’s going to play early.”