The news-making thing to do in 2018 for classic rockers of a certain age is to call it quits.

Or at least say that you’re planning to — once that one last tour is under your belt. Over the winter, Elton John, Paul Simon and Joan Baez all announced they’re hanging up their rock-and-roll (or folk) shoes.

Taken together, the announcements — along with others, like Ozzy Osbourne — send a warning signal to the concert industry.

For years, many of the biggest touring acts have been old reliable baby-boomer rockers like the Rolling Stones, Bruce Springsteen and Tom Petty, who remained huge decades after scoring their biggest hits. Those acts continued to command broad audiences in part because they rose to popularity when the culture was more unified than it is in today’s niche-oriented digital age.

Say goodbye

But those old heads are not going to be around forever. That reality was underscored by the loss of stars like David Bowie, Prince and Petty in recent years, and the grieving their deaths inspired. And as the aging step aside — if they ever really do — is there a next generation ready to step up and fill seats in arenas and stadiums?

Before we get to that question, though, let’s consider another: Can marquee acts with name-brand drawing power ever be trusted when they say they’re going to retire?

Superstar music-makers have been threatening to exit since the beginning of time, it seems, but somehow they always find their way back.

Frank Sinatra retired in 1971, then released “Ol’ Blue Eyes Is Back” two years later. Jay-Z announced he was done with “The Black Album” is 2003 but returned with “Kingdom Come” in 2006.

And, of course, the most egregious offenders are The Who, who first claimed they were saying goodbye for good in 1982, and Cher, whose “Farewell Tour” in 2002 eventually became the “Never Can Say Goodbye Tour” and then … well, she never could say goodbye.

Walking away from the sense of purpose — and the adulation — that comes with entertaining thousands of fans every night on the road isn’t easy. There’s a reason Bob Dylan’s ongoing trek is called the “Neverending Tour” and Willie Nelson is still pretty much living on his hemp-powered bus as an octogenarian. (He turned 85 in April.)

And for every act that makes noise about calling it quits, there are two that refuse to go quietly. Walter Becker died in September, but Donald Fagan isn’t done with Steely Dan. And Fleetwood Mac kicked Lindsey Buckingham out of the band, but their yet-to-be announced tour will go on, with Neil Finn of Crowded House and Mike Campbell of Petty’s Heartbreakers taking his place.

Skepticism abounds. As now 74-year-old Randy Newman told the Telegraph in 2015: “Musicians keep going. There is nobody applauding at home.” Neil Young called the trend “bulls—” and told Rolling Stone, “When I retire, people will know, because I’ll be dead.”

And when Rod Stewart was on Andy Cohen’s Bravo show “Watch What Happens Live” with current touring partner Cyndi Lauper, he was asked what he thought about “your friend Elton” announcing his retirement.

“I did email her and say, ‘What, again, dear?,” he said with a laugh. “I’ve never spoken about retirement, and if I do retire, I’ll just fade away. I think this whole, ‘Oh, I’m going to retire!’ thing just stinks of selling tickets. It’s dishonest. It’s not rock-and-roll.” Lauper, however, suggested they could market their tour as “For the Last Time! Or, Maybe the Second to Last Time!”

They’re really quitting

All kidding aside, though, there’s a seriousness to the retirement business this time around that has to do with chronology and impending mortality. Baez is 77, Simon is 76, and John, whose final jaunt is planned to last three years, is 71. Another hard-touring attraction, Neil Diamond, 77, announced in January that he too will no longer be hitting the boards after being diagnosed with Parkinson’s disease.

The grueling nature of touring is bound to take its toll, as it did on Petty and Prince, whose deaths were painkiller-related. It makes sense that acts like John would park themselves in residencies in Las Vegas, as he has in recent years with — who else? — The Who scheduled to take his place this year.

And though Springsteen’s compulsion to perform hasn’t let up at age 68, he’s found a way to minimize his travel by settling in with a 15-month stint on Broadway.

So, to borrow from a George Jones song, who’s gonna to fill their shoes? The question has arisen during several recent shows at the Wells Fargo Center in which the building had lots of empty seats.

Last fall, Canadian band Arcade Fire, who have carried themselves like heirs to U2 for years, played the South Philly arena and put on a terrific arena-­size show, with one problem: There weren’t nearly enough fans there to fill the arena. More recently, both Lana Del Rey and Lorde did concerts at the venue in which the upper deck was entirely unsold.

(Speaking of U2, the veteran Irish rockers are still more-than-one-night-at-an-arena-size after nearly 40 years in the business. And, like 1990s grunge survivors Pearl Jam, their meaty, earnest rock shows no signs of slippage when it comes to drawing power.)

The smaller-than-optimal crowds didn’t seriously mar the shows. All who came got their money’s worth. But it also served as a reminder that while the concert industry as a whole is going like gangbusters — a record $5.65 billion in global ticket sales came in last year — the need to replace the old heads on their way out isn’t going as smoothly as might have been hoped.

Next headliners

On one hand, the dearth of true new headlining acts has been masked by the preponderance of music festivals. At events like Firefly — which took place in Delaware over the weekend with Pulitzer Prize-winning rapper Kendrick Lamar as one of its headliners — and Made in America, which happens in Philadelphia in September, 50,000 people or so can be lured by the value equation of seeing a dozen or more bands in a single day, and more in a weekend.

On the other hand, while some acts struggle to fill arenas, there’s a group of next-generation headliners that are huge draws.

Among those are arena-size rappers like Lamar and Kanye West, who recently announced a new album and who appears to be ready to tour again. And larger still are acts like Coachella conqueror ­Beyonce.

The list also includes Taylor Swift, country star Kenny Chesney and Swift’s buddy Ed Sheeran.

What all those acts have in common is that they don’t play rock: They’re hip-hop, pop and country stars. After generations in the spotlight, soon-to-be-on-their-way senior citizen baby-boomer stars like John and Simon are finally seeing their epic careers coming to an end and are yielding the communal space to a diverse group of voices making themselves heard.