NEW YORK • This has been a bad year for music legends. First David Bowie, Glenn Frey and Maurice White. Then Prince and George Martin.

In the most recent sobering sequence, Leonard Cohen and Leon Russell.

We have to face it - rock has grown old. Nothing brings out the indignation of a certain kind of rock 'n' roll fan like the suggestion that the music of Little Richard, Jimi Hendrix, Kurt Cobain and other iconoclasts has aged with its audience.

Rock's core audience was born in the 1950s and 1960s and its life span has kept expanding. Sixty years after Elvis appeared on The Ed Sullivan Show, rock concerts are raking in more money than ever.

At the Desert Trip festival in Indio, California, last month, about 150,000 tickets were sold for two weekends of shows featuring six legends of 1960s rock - Bob Dylan, The Rolling Stones, Neil Young, Paul McCartney, The Who and Roger Waters.

The headliners were born in the 1940s. The audience members were of all ages. But growing record sales? Not so much. The record business has evaporated for everyone not named Adele.

Top 40 radio, which has always been for teenagers, is mostly devoted to post-rock pop and hip-hop. This year, rock is not teenage music.

Rock is now where jazz was in the early 1980s. Its form is mostly fixed. From Louis Armstrong in the 1920s to Duke Ellington in the 1930s, to Charlie Parker in the 1950s, to Miles Davis in the 1960s, jazz evolved at super speed and never looked over its shoulder.

In the early 1980s, it began slowing down and looking back.

Trumpeter and composer Wynton Marsalis returned to styles that Davis and Parker had abandoned and showed how much was still there to explore.

Jazz moved into Lincoln Center, established a repertoire and assumed its place as "American classical music". It was no longer controversial or evolving, at least in any popular form.

That is where rock finds itself, in a stage of reflection on past glories. Rock-star memoirs are a booming business. Rock 'n' roll, as we know it, was named in the mid-1950s, born as a mix of black and white musical styles of the Deep South - blues, country and early R&B.

A new invention, the electric guitar, replaced the horn section. The performer was usually the songwriter and there was a standard of honesty, autobiography and (to use a word that was swung like a sword of judgment) authenticity in the rock musician that made him more artist than entertainer.

In the 1980s, rock got a boost from MTV and the compact disc, but the first signs of middle age were already showing.

Rock became the soundtrack to Hollywood movies and television commercials. At the same time, rap began to challenge rock's domination of mainstream music.

After the brief early 1990s insurgency of Nirvana, Pearl Jam and the grunge bands passed, rock became less interested in innovating than in repeating. A popular new rock band tended to sound a lot like beloved old rock bands, and the days when The Beatles moved in a few years from the teen pop of I Want To Hold Your Hand (1963) to the experimentation of Strawberry Fields Forever (1967) were gone.

Certainly, there are rock musicians who push the boundaries of the form. Bjork and P.J. Harvey change the rules with each new album and play to devoted followings - but they do not fill arenas the way even second-tier bands did in the 1970s and 1980s. The musicians who wish to push rock forward are no longer in the mainstream and the rock acts remaining there rarely challenge the old rules.

It is easy to imagine that a musician like Annie Clark, who performs as St Vincent - original, theatrical and a fierce guitar-shredder - would have been a superstar if she had come along between 1966 and 1994. This year, she is a critic's darling with a devoted cult following, sort of like young jazz powerhouse Kamasi Washington.

If rock has settled down, what has taken its disruptive place? Millions of hip-hop fans wait anxiously to see how Kendrick Lamar, Beyonce and Kanye West will surprise them next. Hip-hop's audience still rewards innovation.

Hip-hop has learnt a lot from rock, but hip-hop is not troubled by rock's self-imposed restrictions. Rap songs have multiple writers and do not glorify instrumental soloists; hip-hop stars do not pretend to be uninterested in commerce.

In the late 1980s, when Frank Sinatra was in his 70s - the age the Desert Trip stars are now - white-haired women who had once been bobby-soxers stood at his concerts and shouted, "Frankie, you've still got it!"

Sinatra, a teen idol, had grown up and grown old with his audience.

That is how popular music works. We fall in love with the singers of our youth and the best of them travel with us through life. Sinatra spent his middle years singing songs such as Last Night When We Were Young and lyrics about "the autumn of my years".

Dylan, in his 50s, sang, "It's not dark yet, but it's getting there."

Rock 'n' roll certainly is for old people now. It is for those young people who want it, too. Like any music that lasts, it is for anyone who cares to listen.

And if in 20 years, midlife hip-hop fans are driving through the California desert to see a grey-haired Jay-Z?

As Frank Sinatra sang when the Beatles were on top, "That's life."

The only people who want to die before they get old are those too young to know better.

NYTIMES