“So scared of getting old, I’m only good at being young,” John Mayer belted out during his song “Stop This Train” when he performed at Madison Square Garden earlier this month, part of a world tour that has him at Atlanta tomorrow. Those lyrics feel piercingly true to the 45-year-old singer’s changing role in American music today as a new generation of stars grab the spotlight he once claimed with his award-winning tracks and spate of media controversies.

Mr. Mayer is striking out on a solo tour across North America to revive the songs — and perhaps the popularity — from his “early days.” The star sold out two nights in a row at New York City, which was just the start of his tour, but he has undoubtedly been eclipsed by the likes of Taylor Swift, a former girlfriend whose youth he infamously disparaged. 

Ms. Swift’s net worth just surpassed $1 billion, according to a Bloomberg analysis. The 53 U.S. concerts in her “Eras” tour this year added $4.3 billion to the country’s gross domestic product. The film of her tour generated $92.8 million at the box office in its opening weekend. “Swift Inc.,” Bloomberg wrote, “is essentially a multinational conglomerate with the world’s most devoted customer base, its most charismatic CEO and significant economic power.”

Mr. Mayer is playing a whole other ball game. “I began my career on stage with only a guitar and a microphone,” he said in an Instagram post announcing his acoustic tour. “A lot has changed since then, but I knew one day I’d feel it in my heart to do an entire run of shows on my own again, just like those early days.” Few other pop stars could hit the road without a band behind them and still sell out arenas, evidence of the seven-time Grammy winner’s loyal, yet aging, fanbase. 

The frenzy around Mr. Mayer, though, pales in comparison to that of Ms. Swift. While he has performed in an offshoot of the Grateful Dead for the past year to hundreds of thousands of fans, she has sung to millions during her world tour, which could be the highest-grossing tour ever, far surpassing Elton John’s, just  concluded this year. The average price of Ms. Swift’s pre-sale tickets was more than five times that of the tickets to Mr. Mayer’s concert at the Garden.

This tale of two concerts is a flip of the power dynamic between the two stars during their brief relationship in 2010, when Mr. Mayer was a 32-year-old hotshot in the burgeoning acoustic pop scene, and Ms. Swift was only 19 and new to the music world. “Don’t you think I was too young to be messed with?” she sang of their fling in her song from that year, “Dear John.” Mr. Mayer called the hit dish track “cheap songwriting” and proceeded to write his own in which he likened the young country artist to a “paper doll.”

The criticism surrounding Mr. Mayer’s romantic life only grew after he disclosed intimate details of his relationships with actresses Jennifer Anniston and Jessica Simpson in a 2010 Playboy interview. Ms. Simpson wrote in her 2020 memoir that she was “floored and embarrassed after he called her a “sexual napalm” in the interview — comments which only intensified public ire toward the singer in the wake of the #MeToo movement.

Meanwhile, Ms. Swift’s popularity has been buoyed by her cult-like defenders even as some critics have decried her string of relationships with famous men. The 2022 hit “Anti-Hero” made a mockery of the well-known accusation that Ms. Swift is the cause of her failed relationships. The star sarcastically sings, “I have this thing where I get older but just never wiser.”

As Mr. Mayer has gotten older, the younger and indeed “wiser” Ms. Swift has taken center stage. While he might not have expected to live in her shadow, he seems to have had a prophetic sense when he first met her that her fame was on the cusp of exploding. As he told MTV in 2009, “this Taylor Swift girl is going to be around for a long time.”

Mr. Mayer seems to be accepting the changing of the guard in American music. He had already settled into a quieter life of making music after his notorious years as a tabloid figure in late aughts, and now plans to continue his two-decade-long career by leading the Grateful Dead legacy and its older fanbase after the original members pass away. 

 Yet Mr. Mayer appears to relish in reliving the glory days of his past, if only for a couple hours on stage. Of his need to play his “old songs,” he expressed on Instagram, “it took a couple of decades, but I feel it now.”

With an air of wistfulness, Mr. Mayer told the crowd at the Garden, “things come and go, songs come and go — just like youth.” After more than two hours of singing the dozens of melodies that propelled him to fame, the star grabbed his microphone and screamed out to the fans as they began shuffling out of the arena: “Because of you, I still get to be John Mayer.”