Elvis and Priscilla, Demi and Ashton, Tom and Katie — they all seemed blissfully happy in those early years, despite the fact that more than a decade separated them in age. Both men and women who pair up with much younger spouses often initially exhibit a noticeable happiness. It’s hard not to wonder if the secret to a happy marriage is finding someone out of your age group.

According to new research, people who have partners several years their junior do indeed experience greater satisfaction in the beginning of a union than same-age couples. But the honeymoon doesn’t last forever — six to eight years at the most. Age isn’t just a number, after all, which may explain why so many celebrity May-December marriages end in divorce.

Researchers compiled 13 years’ worth of data from the Household, Income and Labor Dynamics in Australia (HILDA) survey comprised of 8,682 households with 19,914 individuals. Every year participants were resurveyed about their life satisfaction. They found that men with younger wives are the most satisfied initially, while men married to older women are the least. “Women are also particularly dissatisfied when they’re married to older husbands and particularly satisfied if they’re married to younger husbands,” says Terra McKinnish, an economics professor at the University of Colorado Boulder and a co-author of the study.

However, after six to 10 years of marriage these “big age gap” couples aren’t quite on cloud nine as satisfaction dissipates. “The people who are married to a much older or younger spouse tend to have larger declines in marital satisfaction over time as compared with those who are married to spouses who are similar in age.”

It may come as zero surprise that a potential reason for this decline in overall happiness could have to do with money. The couples with several years between them didn’t seem to handle economic shock, such as the loss of a job, quite as well as same-age couples. McKinnish believes this is because couples around the same age are more in sync about where they are in life (having children, how they spend and save, etc.), while big financial shocks could reveal underlying issues and mismatches with the age-gap couples, who didn’t have much in common in the first place.

A 2014 Emory University survey of married couples projects a similarly dismal outlook for May-December romances. According to an analysis of 3,000 married couples, the bigger the age gap between a couple, the more likely they are to split than same-age couples. For instance, couples with 10 years between them were 39 percent more likely to split than a same-age couple, while those with a 20-year gap were 95 percent more likely. Couples with a 30-year differential were pretty much doomed: 172 percent more likely to end up divorced.

While statistics don’t seem to support marriages with large age gaps, the heart wants what it wants — and it’s unlikely that any scientific research, no matter how convincing, will prevent someone from falling in love with a much younger person.

Do you think May-December marriages are doomed? Are you surprised by the findings of this research? What other factors play into the deterioration of satisfaction for couples with a huge age gap?