Quarterback Patrick Mahomes, the Chiefs’ first-year starter, threw for four touchdowns in a season-opening victory. (Harry How/Getty Images)

Early Sunday afternoon, New England Patriots quarterback Tom Brady took the field at Gillette Stadium to begin his 19th season in the NFL. His counterpart, Deshaun Watson of the Houston Texans, lined up behind center five days shy of his 23rd birthday.

Later in the day, Patrick Mahomes would sling sidearm darts, launch effortless deep balls and erupt into the NFL’s newest sensation in the Kansas City Chiefs’ win over the Los Angeles Chargers and quarterback Philip Rivers, 14 years his senior. At night, Aaron Rodgers performed feats of magic for the Green Bay Packers and stole a victory from the Chicago Bears’ Mitchell Trubisky, who was 10 on the day Rodgers was drafted.

Across the NFL, Week 1 showed the state of quarterbacking in the league. The 2018 season will give the NFL an uncommon constellation of signal callers — a mixture of familiar faces, future Hall of Famers and exciting young passers. It will give the league, in other words, exactly what it has been hoping for — and trying to engineer — for the past two decades: a golden age, of sorts, of quarterback play.

For 20 years, the NFL has passed rules changes designed to make playing quarterback safer and easier. It has banned late hits, high hits and low hits on quarterbacks, along with several types of hits on receivers. The effects of those changes, now that an era of quarterbacks has played an entire career under them, have become evident.

Quarterbacks in their late 30s — such as Brady, Rivers and the New Orleans Saints’ Drew Brees — aren’t aging out of the league at the same rate as their predecessors or even declining in performance. As young quarterbacks come into the league, they’re adding to the pool of useful quarterbacks more often than they’re being forced to fill in. Good quarterbacks are being displaced, not replaced, and therefore are in deeper supply.

We’re essentially watching two or three mini-generations of quarterbacks at the same time, all able to play at a high level based on health and conditions that make it easier to succeed. Old quarterbacks stay healthier longer, and young quarterbacks can adapt to the league faster.

“In all honestly, I don’t think we would have predicted the longevity some of these fellas have had,” said former NFL executive Bill Polian, a longtime member of the league’s competition committee. “But clearly, clearly, we were trying to keep our quarterbacks upright and healthy as best we could.”

In Week 1, 10 teams started quarterbacks who are 33 or older, six of whom have won a Super Bowl and another who has played in one. The NFL thrives on that kind of star power and familiarity. When ratings dipped two years ago, the NFL cited Peyton Manning’s retirement as a significant factor.

“I talk to players at other positions all the time,” Polian said. “I was talking to a fullback this summer. He said: ‘Ah, we’re making too much of these quarterbacks. There’s 21 other guys [on the field for each play].’ I told him: ‘Yup, that’s exactly right. I couldn’t agree more. But that’s not why people tune in.’

“There’s no question the rules, their application by the officials and sports science and medical science and exercise science and dietetic science have lengthened the careers of the elite quarterbacks. But that’s all to the good. The more we see of Tom Brady, the better. The more we see of Drew Brees, the better.”

A handful of quarterbacks hanging around for a few extra seasons can make a significant difference in the NFL’s quality of play and drawing power. Remove, say, the Pittsburgh Steelers’ Ben Roethlisberger (36) and the New York Giants’ Eli Manning (37), and the complexion of the NFL feels different. Consider it like this: If John Elway and Troy Aikman played until their age-41 seasons, they would have overlapped with Brady.

While rules changes have afforded more quarterbacks the health to stay in the league, they’ve also made it easier for quarterbacks entering the league to learn and find success. Seven teams started a quarterback in his first three seasons Sunday, and all but Nathan Peterman of the Buffalo Bills stands a reasonable chance to become a long-term answer with short-term success. That doesn’t count the Philadelphia Eagles and Carson Wentz, one of the league’s emerging stars who is still recovering from a knee injury. In his place for last Thursday’s opener, Philadelphia started Nick Foles, a backup most of his career who led the team to the Super Bowl last season, winning the game’s MVP award.

A shift in coaching philosophies has helped the young cohort, too. Coaches have been more willing to adopt concepts borrowed from the college game — including up-tempo pace, aggressive spread formations and run-pass options — and suit schemes to fit quarterbacks. The Los Angeles Rams’ Jared Goff looked like a bust during his rookie year under Jeff Fisher, but playing for Sean McVay in his second season, he suddenly morphed into a franchise pillar while leading one of the league’s most potent offenses. Trubisky has a chance to undergo a similar upgrade, having traded John Fox for Matt Nagy, a progressive Andy Reid disciple who was hired by General Manager Ryan Pace for the primary purpose of helping Trubisky succeed.

Goff, Watson and Mahomes are among the players who came from college offenses that were previously viewed as not providing quarterbacks with the preparation necessary to succeed at the next level. As the NFL has come to more closely resemble college football, and young quarterbacks have adapted to the pro game more quickly, those concerns have been lessened.

The combination of aging stars and emerging passers has created rare contentment. Despite an unusual amount of quarterback movement this offseason — the Denver Broncos, Washington Redskins and Minnesota Vikings added a veteran who ranked among the league’s better passers a year ago — the majority of teams are satisfied with both their present and future quarterback situation.

“Almost every team knows who their guy is, or believes they know who their guy is,” CBS analyst Boomer Esiason said.

And there are more on the way. Five quarterbacks were selected in the first round of this year’s draft, including four in the top 10 picks, and yet only one started Week 1, and just two played.

Rules changes are not the only reasons quarterbacks can play longer, but they have helped exactly how the NFL envisioned. Even just a few seasons ago, there was concern that the league didn’t have enough quarterbacks. It does now, mainly because the ones who were carrying the league then haven’t gone anywhere.

“The successors are on the horizon,” Polian said before noting that even the most successful among the latest generation of QBs haven’t quite eclipsed the league’s superstar veterans. “But that’s okay. I’d rather have the king still on the throne.”

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