On a cocktail napkin, she wrote A real kiss. He wrote Sex and clarity.

The pair had been seeing each other every couple of months for about a year. After dinner or the opera, they'd typically end their dates with a hug. One night the woman suggested that they each write down what they would like if they beat the other in a game of pool.

After he won a game, her date revealed a napkin saying he wanted to be friends with benefits. He was divorced and wasn't ready for a relationship. "That's fine," said his date, Helen Fisher, Ph.D., a biological anthropologist and senior research fellow at the Kinsey Institute at Indiana University. But "once you start to have sex with somebody, it can trigger the brain circuitry for romantic love.

Are you willing to take that chance?" she asked.

"He said yes, and one thing led to another," says Fisher, 78. They married three years ago.

If you're not intimately involved in the complicated, hot, playful dating lives of those over 50, you may be curious about what it's like to be one of the many who are starting over after divorce or the loss of a spouse. In fact, 29% of people ages 50 to 64 are single, as are 33% of those who are 65 and older, per the Pew Research Center.

While the dating pool may be of a different depth and shape than the one some swam in decades ago, the water is still fine if you're willing to jump in.

the NEW RULES of dating

Falling head-over-heels is ageless, and Fisher and a team of researchers proved it. They put people in their 50s and 60s into a brain scanner using fMRI (functional magnetic resonance imaging). "When they're madly in love with somebody, their brain scans show exactly the same pathways for romantic love as in people in their early 20s who've just fallen in love," she says.