Marianne attributes many women's reluctance in growing older to what she calls "youthitis." "The breasts were higher, the butt was firmer, blah, blah, blah, and then this reality [sinks in] that I'll never have it again," she says.

Spending time wishing you were younger prevents you from enjoying the present moment. "I think sometimes as we get older in a society like ours, we go around relating more to what we are no longer than to what we are," Marianne says. "In everything in life, there's something about allowing yourself to be in the experience and allow yourself to receive the gifts that it brings you."

Marianne says pining for the past or the future doesn't begin in the 40s or 50s—most people do it all along. "We didn't appreciate what we had when we had it. We thought we needed a different career, a different husband, a different boyfriend, whatever," she says. "It's all the activity of the mind that 'whatever' is isn't good enough, and so you have the feeling you miss so much of your youth."