LOS ANGELES — As “American Idol” winds down its 11th season, it’s time to ask: Is Fox’s smash singing contest losing the kids?

For years, “Idol” was TV’s unrivaled ratings champ, and a big part of its success lay in its appeal to young people, who made it their No. 1 TV choice for years. But this year, critics are attacking the show as increasingly stodgy while viewership has plunged more than 30 percent among teens and twentysomethings. And many of those viewers have gone to NBC’s “The Voice,” a hipper and sexier upstart that has much younger judges and often edgier songs.

“The Voice” has pulled even with “Idol” in ratings among young adults and has a median age of 43, according to Nielsen. Though not exactly brimming with youth, that figure nevertheless beats “Idol,” which has a median viewer age of 48 — 14 years higher than it was when the show premiered back in summer 2002.

“’Idol’ is indeed aging and it will likely never regain the ratings it once boasted,” said Jeffrey McCall, a communications professor at DePauw University. “’The Voice’ has surprised me with the traction it has generated. It really does come off as younger than ’Idol.’”

The financial stakes are enormous, because advertisers pay the most for young eyeballs. “Idol” earned $688 million in advertising revenue last year, down 7 percent from the previous year, according to an estimate from research firm Kantar Media. By comparison, “The Voice” racked up just $57 million because it was a new show with no track record and also because it lasted well into the summer, when viewing is lower. Nevertheless, “The Voice” has revived NBC’s prime-time prospects and speculation has it that the show will return in the fall, although the network has confirmed nothing.

Meanwhile, signs that “Idol” is undergoing a midlife crisis have been piling up.

Shortly after he was voted off the show, Heejun Han, a 22-year-old New Yorker with a deadpan sense of humor, joked that he wasn’t going to root for any of the remaining contestants and would just watch “The Voice” instead. It was a mischievous remark that popped the bubble that surrounded “Idol” semifinalists of years past, when the show was a cultural superpower without peer.

Following the exit of “mean judge” Simon Cowell at the end of Season 9, the “Idol” judges have focused on being nice to contestants, with trenchant criticism the exclusive province of 59-year-old mentor and record mogul Jimmy Iovine, who appears in taped segments. After a recent performance by young hopeful Jessica Sanchez, judge Steven Tyler said, “Everything you do is beautiful” — a warm sentiment that neither offered any clues as to how she might improve her chances of winning the competition nor supplied the sort of friction that makes for good TV.

Among the judges, “Idol” and “The Voice” have a wide generation gap. “Idol’s” troika of Tyler, Jennifer Lopez and Randy Jackson has an average age of 53, quite old for a show that seeks relevant pop-music stars. On the NBC show, judges-mentors Christina Aguilera, Adam Levine, Cee Lo Green and Blake Shelton are all in their 30s.

“Steven Tyler is a senior citizen and Randy Jackson is well into his 50s,” said McCall. Indeed, the gossip site TMZ recently underscored Tyler’s advanced age with a picture of the 63-year-old rock star ambling on a beach in Hawaii, with a close-up of his hammertoe, a foot affliction commonly seen among the elderly.

And “Idol” has stuck to its practice of “themed” performance nights, even if that means picking oldies made famous long before any of its contestants were born. “The Voice” has tended toward some unusual, even risky choices: A recent episode showed contestants preparing Nirvana’s ominous ballad “Heart-Shaped Box.” “Idol” meanwhile, recently did a night devoted to songs by Billy Joel, who was considered middle-of-the-road even in his 1970s heyday.

“Billy Joel hasn’t released a new pop song since 1993,” Rodney Ho, who has blogged about “American Idol” since the show premiered, wrote in an email. “Half the singers on ’Idol’ weren’t even born yet!”

For its part, Fox declined to comment directly for this story, other than to issue a prepared statement. “After 11 seasons, ’American Idol’ is still the gold standard for competition shows on television,” the statement said. “No other series in TV history has discovered and launched so many bona fide stars across music, television, theater and film, or shaped the culture in the way ’Idol’ has.”

An NBC spokeswoman said: “The ratings are proving there is clearly room for both ’The Voice’ and ’American Idol’ to not only coexist but thrive as well. And on top of that, advertisers enjoy the family-friendly environment that these shows offer and the opportunities to integrate their clients into them seamlessly.”

Analysts agree that the war of the singing shows may not end anytime soon. But “Idol” may have to fight with far fewer kids on board than in the past.

“’The Voice’ does seem to have that ’cool’ factor now, but ’cool’ in TV can be quite fleeting and solid ’mainstream,’ like ’Idol’ has become, can still provide long-term success,” said McCall.