New York ? As a 20-something, Erin Turner feels she made all the right moves dating wise. She graduated from college and spent three and a half years with a boyfriend before they moved in together.

Their cohabitation bliss lasted only eight months.

“We broke up because when you live with someone, everything comes to the surface,” said Turner, who remains single in Chicago as her 30th birthday approaches in March.

“You start to see how people handle confrontation, financial realities, challenges, the housework load. If we had been married, we would have been divorced, or fully on our way.”

While Turner hopes to marry one day, she’s not sweating it at the moment. Her parents divorced when she was young, and she doesn’t want marriage badly enough to settle. She’d be sad if she never married, but she wouldn’t “implode.”

Heading into 2012, trend watchers note that barely half of all adults in the United States are married, and the median age at the time of a first marriage has never been higher: slightly more than 26 years old for women and nearly 29 for men.

In 1960, 72 percent of those 18 or older were married. The percentage fell to 57 percent in 2000, and today it’s just 51 percent, according to a new Pew Research Center analysis of census data.

The share of marrieds could dip below half in a few years as single-person households, single parents and couples living together outside the bounds of legal marriage multiply. The number of new marriages in the U.S. fell 5 percent just from 2009 to 2010, a wrinkle that may or may not relate to the bad economy, Pew researcher D’Vera Cohn said.

The decline is spread among age groups but is most dramatic among Turner’s generation. Nearly three out of every five adults ages 18 to 29 were married in 1960, but now only one in five is.

Marriage also is on the decline in other developed countries, especially those in Europe, and the trend is starting to take root elsewhere around the globe.