Supposedly, young adults don't have much of an attention span — except when it comes to love.

That's when it seems this generation of young people is giving new meaning to the words "long-term relationship." Many are "a couple" for years, and some approach a decade of dating. They're just shy of the altar for so long that parents and grandparents are a bit bewildered.

"It's good to get to know your partner before marrying, but one wonders how long you need," says sociologist Andrew Cherlin, 61, of Johns Hopkins University.

Relationships today are far different from the whirlwind courtships that blossomed in the uncertain 1930s and '40s. Lyndon Johnson and Lady Bird met in August 1934, and he proposed on their first date. They were engaged in October and were married in November.

Prince William and Kate Middleton are perhaps the most visible example of today's couples. There's speculation about an impending engagement of the son of Britain's Prince Charles and Princess Diana, but the fact remains these 28-year-olds are in their ninth year together. On Saturday, Sweden's Crown Princess Victoria, 32, married her beau of eight years.

In the post-World War II era, couples married in their early 20s. Now, it's 28 for men and almost 26 for women, Census says.

Among those of marriageable age today, a delay in tying the knot doesn't mean they haven't paired off; it just takes some time to seal the deal.

"We wanted to see that we could function in a domestic environment — live together and work together and share responsibilities, so there wouldn't be any surprises," says Aubrey Clayton, 30, of New York City.

He and his fiancée, Melissa Tapper Goldman, met in 1999 at the University of Chicago. They each moved around the country; he to California for grad school, she to Boston and then Albuquerque. But they kept in touch. Each had been in a long-term relationship that ended before they started dating in January 2005. They were engaged five months ago.

Goldman, 29, a documentary filmmaker, says a lot has happened in five years. Clayton finished his graduate studies in May 2008, but it took a year to find a job as a mathematical consultant. In May, Goldman completed a master's in architecture at Columbia University. And, they just moved to a new apartment.

"It was important to me that Aubrey and I could see each other through a life change and feel good about being together," she says. "Change after change made me more secure knowing this was someone I could go through a lot of changes with."

That kind of thinking makes sense, experts say.

"There's a certain wisdom in lengthy courtships," says Gary Hoppenstand, professor of American Studies at Michigan State University. "If it lasts three, four, five, six or seven years, they feel like there's something there to support a marriage that will last."

Michael Johnson, emeritus professor of sociology at Pennsylvania State University, says the combination of a certain maturity level and the ability to work out problems before committing may help young people avoid the marital mistakes of the Baby Boomer generation.

The world has changed so drastically that experts say today's young adults have a lot to ponder, much more than decades ago. More education has meant delayed financial independence, which is a major reason young adults say they aren't making their relationships official.

Other reasons: Sex before marriage is widespread; two-thirds live together before saying "I do." And there's a whole world of other potential partners yet to meet. Though movies and TV portray perfect romances, these young adults worry about divorce — they know some relationships just don't last.

"There's a lot of fear percolating around marriage," says Hannah Seligson, 27, author of A Little Bit Married, a book about serial long-term relationships and cohabitation released earlier this year. "They want to get it right."

Hoppenstand, editor of The Journal of Popular Culture, says society sends mixed messages: "This romantic ideal perpetuated in popular film and TV — 'finding the one true love and the love that will last a lifetime' — vs. celebrity culture — 'married and divorced and married and divorced and multiple mistresses.' Day after day, it promotes this instability of romantic connections."

Goldman agrees. "You get all this sage advice in movies: 'You'll just know the one.' Those are not useful pieces of advice."

Most expect to marry

Still, most young people do expect to get married and believe they will stay married. A 2008 report from the University of Michigan, based on a survey of 2,300 high school seniors across the USA, found that 80% say they will marry and believe they'll stay married to the same person for life; 4% say they won't marry. The rest aren't sure.

Money worries are a significant factor in delaying marriage.

"Just getting out of college, I'm thinking 'She's probably the one,' but I didn't have any financial stability. I wanted to have some foundation before I asked some chick to be with me forever," says James Marsden, 25, a financial adviser in Dallas, who says he and girlfriend Brittney Locey, 25, probably will get engaged this year. "When I started working, I felt like what I was building at work was for us," he adds.

Locey, who works in customer service in aerospace sales, says they started dating in 2001 when she was 16. During that period, they broke up a couple of times and dated others.

Such on-again/off-again relationships are a new area of research, says René Dailey, assistant professor of communication studies at the University of Texas-Austin.

Although breaking up and getting back together has been considered a bad sign, she has found some couples benefit from one or two breakups. Dailey says many "redefine their relationship"; some change things about themselves or about the relationship and report resolving whatever problems they had.

"It used to be, if they broke up, it's over, and the relationship is done," says Dailey, co-author of a study published in March in Communication Monographs.

This back-and-forth reflects a desire among some to keep their options open, experts say.

"They may still have this feeling they don't want their possibilities constricted. 'I love this person and am committed to him or her, but I don't want to say this is it yet. I want to have the feeling if I did want to do something else, I could do it,' " says psychologist Jeffrey Arnett of Clark University in Worcester, Mass., who studies emerging adulthood.

Psychotherapist Shannon Fox of Branson, Mo., co-author of Last One Down the Aisle Wins, says these young adults don't date seeking "marriage material."

"They think, 'This works now. It feels right for now,' " she says. "This is the generation that won't commit to going to a party on Saturday because something better might come along — someone better might come along."

Cherlin doesn't expect this pattern to change unless Americans want more children than they're having now.

"If all you want is one or two kids, you can wait until your 30s to get married," he says. "We may in the future look more like France and the Scandinavian countries, where many couples live together a long time before marrying. And a lot of them have kids."

Money matters

Even young people who marry early by current standards take their time in the courtship phase. Amber Duke, 28, of New Albany, Ind., dated her husband, Brent, 29, for more than five years before they married five years ago. "We celebrated 10 years together this past March," she says. "It has felt like Brent and I kind of grew up together."

Carrie and Brandon Wallace of Denver, both 26, grew up in Upper Arlington, a suburb of Columbus, Ohio. They met as high school freshmen and started dating at the end of the school year.

They went to the same college and "broke up twice, maybe for a week," says Carrie Wallace, a regulatory affairs analyst. They married last summer. "We wanted to have our careers established and be financially stable on our own," says Brandon Wallace, a commercial banker.

He says he got a promotion in 2008, which gave him the confidence to get engaged. "I didn't want to drain our savings to buy a ring and the condo. I actually proposed the night we moved into the condo," he says.

The cost of weddings is something all couples think about, whether they are middle class or working class, says Cherlin. "Marriage has become the symbol of a successful personal life. They want a party to show themselves and others that they've really made it."

Dallas attorney Nicole Tong, 28, got engaged in December, after dating her fiancé, 30, for 51/2 years. They just bought a house. But she says the wedding won't be until March 2013.

It will be a small gathering of at most 50, she says. "We don't want to go into debt for a wedding."

Tong says they don't plan to have children, so there's no rush:

"We're just really in no hurry, and we want to make sure it's everything we want."