MILEY CYRUS, HILARY DUFF AND OTHERS ARE TYING THE KNOT. ARE THEY IMPULSIVE? BOUND FOR DISILLUSION? OR JUST TRYING TO LIVE NORMALLY?

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Actor Liam Hemsworth and singer Miley Cyrus.

Miley Cyrus likes to spend her days playing with her dogs, skateboarding and watching television marathons of "SpongeBob SquarePants" — activities she often chronicles on Twitter. Now, the 19-year-old will have to fit a more adult activity into her schedule: wedding planning.

The singer-actress announced last month that she is engaged to 22-year-old "The Hunger Games" star Liam Hemsworth. She becomes the latest in a line of young Hollywood stars to head for the altar, even as Americans are marrying older than they used to, and many are skipping the nuptials all together.

Hilary Duff — who like Cyrus starred in her own show on the Disney Channel as a teenager — married at 22 and had a baby in March at 24. Three years ago, the eldest member of the sibling boy band the Jonas Brothers, Kevin, wed at 22 and next month will star in an E! reality show about settling into married life. And though he has yet to pop the question, 18-year-old pop star Justin Bieber has been in a serious relationship with tween queen Selena Gomez, 19, for nearly two years.

This mini-outbreak of traditional wholesomeness stands in stark contrast to the drumbeat of tabloid tales of debauched young stars: Lindsay Lohan drunkenly stumbling out of yet another nightclub, Shia LaBeouf getting into a succession of bar fights, Vanessa Hudgens taking nude photos of herself (which subsequently leaked onto the Web). Yet news of these fresh faces tying the knot often is met in the media with skepticism if not outright ridicule.

"I hope she got the bong I sent her as a little [engagement] gift," Joy Behar joked about Cyrus on "The View," alluding to a video that surfaced in 2010 of the teen star smoking from a water pipe. "I regretted getting married at 22. ... Do not get married so young."

So why the rush up the aisle for some young celebrities, when the average American woman waits until 27 and men until 29? Industry observers and marriage experts say there are various forces at work: First, many of these stars come from religious or cultural backgrounds in which it's more acceptable to settle down early. They've also had professional responsibilities since they were children, forcing them to interact with adults and possibly mature more rapidly. Plus, as fame and income increase, stars have a harder time finding people they trust — so when they do, they hold on tight.

"Everything came so fast for me," Duff said by telephone last month, the sound of her infant son crying in the background. "I was financially secure and successful at my job and having to take on a lot more responsibility than the average 18-year-old. Plus, I feel like being in the dating world was never an option for me. I wasn't going to give just any person my number. I didn't have an opportunity to meet people outside of the business."

Bonnie Liedtke, a manager whose former clients include Zac Efron and Leonardo DiCaprio, says the young stars she works with are often worried about socializing outside of small groups for fear of being exploited.

"Being in this business tends to drive people to a smaller scope," said Liedtke. "People feel like they can only trust very few people now with social media and having photos taken in private situations. Dating somebody outside of that small circle can become very difficult."

Duff, who starred in the television series "Lizzie McGuire" from ages 16 to 19, met her husband, former professional hockey player Mike Comrie, through a trusted mutual friend. Once the pair began to develop strong chemistry, Duff said she experienced a level of ease with Comrie that she had never before experienced.

"When you're so well known, you're also extremely secluded. You don't have a normal life, and so when you find someone that you just love to be around and you're in love with and totally compatible with, there's so much a sense of comfort," she explained.

But Duff made her name off her squeaky-clean image, and the majority of her fans were girls who aspired to be her best friend. Kevin Jonas had a similarly lily-white image, but there was far more at stake for his career when he decided to tie the knot with former hairdresser Danielle Deleasa. The Jonas Brothers — who were propelled to fame by the admiration of females — were at the height of their popularity and about to release their fourth album.

"Obviously, you don't know how fans are going to respond," the singer admitted during a recent break in filming his new television show. "So we said, 'Let's hold the engagement news for two weeks after the release.' That was the one safety." The album went on to sell nearly 250,000 copies and peaked at No. 1 on the Billboard 200.

Liedke acknowledges that she has often urged young male clients to hide details of their romantic lives so as not to taint their heartthrob images.

"Unfortunately, the demographic that male stars attract is a younger one that likes to fantasize, and by saying you're married, it can affect your career," she said. "A relationship is one thing, but to be married at 20 — to the fans that think they're going to marry that person, it's a big deal."

Throughout the years, a number of celebrities have kept their romances close to the vest so as not to upset fans. When a 21-year-old John Lennon married his first wife, 22-year-old Cynthia in 1962, the Beatles' manager Brian Epstein urged the couple to keep their nuptials a secret. To keep fans at bay, Epstein even rented a private hospital room for Cynthia when she gave birth to the couple's son, Julian, the next year.

Although few stars go to such extreme lengths today, many are cagey with the press about their private lives. Kristen Stewart and Robert Pattinson, the stars of the "Twilight" franchise, have been rumored to be dating since the series launched in 2008. Still, neither has ever publicly confirmed the relationship, and they've avoided engaging in public displays of affection.

As for Bieber, when pictures surfaced of him kissing Gomez on a Hawaii beach last year, the"Wizards of Waverly Place"actress initially received death threats via Twitter. But Bieber doesn't seem to have suffered any major career backlash. Once his rabid masses cooled off, the pint-sized musician's career wasn't any worse for the wear: In the last year, he banked $55 million, according to Forbes.

"For generations, the general feeling has been that young stars who are teen idols should be single because that helps to build their image," said Bradley Jacobs, a senior editor at US Weekly. "But Justin Bieber's relationship with Selena Gomez flies in the face of that — he's been dating her for a long time, and it hasn't hurt him at all."

Bieber's manager, Scooter Braun, recently told Rolling Stone he felt the singer's relationship with Gomez actually helped his image. "[G]irls that see him with a girlfriend, hear about the romantic things he does and want him even more," Braun said.

Bieber and Gomez, like Cyrus and Jonas, are devoutly Christian. Jonas and his brothers famously wore purity rings as teenagers, while at 16 Cyrus proclaimed her intention to remain a virgin until marriage in keeping with her Christian faith. Duff, Cyrus, Jonas and Gomez were all born in Texas or Tennessee, and "young adults from the South and those with more religious backgrounds are more likely to marry earlier," according to Bradford Wilcox, director of the National Marriage Project at the University of Virginia.

"There's a stronger cultural religiosity there," Wilcox said. "Even for people who aren't devout, they're embedded in a milieu that tends to view marriage at a young age as socially acceptable."

Even so, the odds for those who marry young are bleak: Roughly 60% of couples who marry between 20 and 25 divorce, according to the National Center for Health Statistics. That's likely at least in part because the human brain isn't fully developed until age 25 or 26.

"We feel quite grown up as young people, but neuroscientifically, we know the brain is still continuing its development through the early 20s," said Dr. John Sharp, a faculty member at Harvard Medical School. "The parts of the brain that control impulsivity — the speed of processing that leads to judgment — is continuing to improve."

Despite the science, Sharp believes stars like Cyrus may not be making a mistake in marrying young.

"If the choice is between sowing one's oats and getting into trouble with excesses, then this looks like it could be a healthier choice," he said. "You find someone you trust and hold on to them tight, and maybe you don't have to go through those difficult, dangerous years where people fall prey to substance abuse."

Jonas, whose new show "Married to Jonas" premieres Aug. 19, said he's eager for skeptics to get a behind-the-scenes glimpse of his relationship.

"Early on, people would say, 'Give them two years and they'll be over.' But we've outlasted all the haters," he said. "There's so many people that take pride in being a mom, and it's odd to me that young celebrities [like Duff] get backlash for wanting to pursue the things that are normal in life."