Karen Bigman, Midlife Sexpert

Testosterone peaks in a man's twenties and declines gradually from around age 30 onward.

Picture two men, both married roughly twenty years, both facing the same quiet gap in their sex life. Their marriages look nothing alike from the outside. The mistake underneath is nearly identical.

Every man who's watched his wife's desire fade has built a story to explain it. Usually the story centers on him: he's not attractive enough anymore, he waited too long to fix things, she's simply done wanting him.