The loosening of relationship conventions, which is not limited to age but also includes race, religion and economic status, appears to be particularly evident among female baby boomers, sociologists say, who are faced with the tightest “marriage squeeze”  the smallest pool of compatible men as conventionally defined, those two to three years older, of similar background and higher levels of education and income. The reason is that as women have delayed marriage, men still have a tendency to date and marry younger women.

In the last several years, as the loaded term cougar was popularized by the media’s frenzied fascination with Demi Moore’s marriage to Ashton Kutcher, 15 years her junior, and the dalliances and liaisons of other celebrities like Madonna and Katie Couric, researchers have begun to examine the older woman-younger man relationship. It is one that has long been taboo, heavily influenced by the Freudian notion that the older women are mother substitutes or “robbing the cradle.”

“For a long time we’ve been fed this idea that women should look for a man to take care of her, a man that is more educated, has a better job and makes more money,” said Sandra L. Caron, a professor of family relations and human sexuality at the University of Maine. “That might be fine and dandy if you’re in high school and have this fairy tale Prince Charming. But when you look at adult women, most are self-sufficient and they don’t have to look for that.”

Dr. Caron is an author of a 2006 study of couples in which the wife is at least 10 years older, which found surprisingly positive attitudes among the couples, although fear of stigma and insecurity about aging for the women, in particular, were common.

The study, published in the Journal of Couple and Relationship Therapy, reported that the couples thought their age difference mattered more to the outside world than to them, and that the men were more strongly drawn to the relationships at the start because of physical attraction.