Demi Moore and Ashton Kutcher: Doomed by the Age Gap?

May-December relationships can be challenging for the older woman.

Sept. 24, 2010— -- As the tabloids pull out the big guns claiming Ashton Kutcher cheated on Demi Moore, People Magazine published a celebratory photo gallery, "Ashton and Demi: Inside Their Marriage," tied to the couple's fifth anniversary today.

But as more people ask, "Did he or didn't he?" perhaps an equally valid question is whether their union was compromised from the start by the dates on their birth certificates.

The minute Hollywood couples tie the knot, rumor mills start looking for them to untie. May-December unions – especially when the woman is considerably older than her man – are real game changers.

Is the age gap – Moore is reportedly 15 years older than Kutcher – the likely fuel that incites a younger male partner's extramarital flings?

"Age is generally not at the top of the list for adultery," said Helen Fisher, a biological anthropologist, expert in human sexuality, and author of "Why Him? Why Her? Finding Real Love by Understanding Your Personality Type."

Fisher, who has studied adultery in 42 cultures, said many factors – boredom, loneliness, relationship conflicts, a desire for more or supplemental sex, available women, and looking for a way out of the relationship by getting caught – lead people to look for flings.

"After a man falls madly in love, he no longer cares how old she is," said Fisher, who's also chief scientific advisor to, whose matchmaking is based on a personality test she developed. "Love is extremely powerful, and can overcome tremendous barriers, including age, even though the rest of the world unconsciously tends to equate stable relationships with the woman's ability to bear children."

"Demi Moore and Ashton Kutcher have been the poster couple for healthy older-women May-December relationships," said Ian Kerner, a sex therapist in private practice in New York and author of "She Comes First." "They appear affectionate and loving, enjoy family events and he's considered a father figure and role model to her children."

Demi Moore and Ashton Kutcher: Do May-December Romances Last?

But, cautioned Kerner, "Infatuation does a lot of the work in the beginning of the relationship." As time goes on, challenges increase. "It's harder to form friends in common and maintain the same values. Maintaining sexual interest is also more difficult. Men tend to cheat more opportunistically."

Joyce Morley-Ball, a relationship expert in private practice in Atlanta, said that a woman in this type of relationship is vulnerable. "She's always asking herself, 'Can I keep a younger woman at bay?' She'd have to be very secure to not constantly have to look over her shoulder."

Terri Orbuch, a social psychologist in Detroit and a professor at the Institute for Social Research at the University of Michigan, has interviewed many older women who worry about the cultural and media message that equates youth with sexuality and beauty. But the bigger danger in the survival rate of younger-men and older-women couplings is the waning of similar interests, she said.

"Although they may have similar interests when they marry, change is inevitable," said Orbuc, author of "5 Simple Steps to Take Your Marriage from Good to Great." "When the woman is older, her life transitions, often in terms of career recognition or children, often result in changes of values. Unless the couple consistently and consciously works at making similarities happen, then a man may gravitate to people with more similar interests and attitudes."

"Unfortunately," said Orbuch, "the loss of similarities is more likely to happen when there's a big age difference in the relationship."