I wasn’t alone in this longing. A whole generation of strong, accomplished baby boom women were feeling something similar, or at least that’s how it seemed from my own privileged corner of the world.

But why do we feel this way? Are we longing to get back to our own youth, when not only were our babies bundles of infinite possibilities, but we ourselves were, too? Is our longing more altruistic, a hope for our children to know the deep joy that comes from being a parent? Are we just bored and looking for something meaningful to do?

In many ways, grandbaby lust is a lot like the baby lust of younger women, with the same uncertainties of fertility, desire and commitment. But there is one agonizing difference: They are not your uncertainties to work out. They’re your son’s or daughter’s. And these sons and daughters often think that they have all the time in the world.

While we, the would-be grandparents, know that our own time is running out.

In the last few years of her life, my mother would talk about the angst of aging. Who’s that old lady in the mirror? she’d say, thinking she was being clever. And, more seriously: Why does no one need me anymore? When did I become unwanted, or, as the French would say, de trop?

I was impatient when she said these things. Everyone feels that way, I would tell her . It was almost the cruelest thing I could have said to my brainy mother, that her conversation was a bit of a cliché.

She died last year at the age of 92, and my impatience with her feeling de trop is one of the things I feel most guilty about. Why did I have to be so brusque? She was just trying to connect, to state an emotional truth that’s a cliché precisely because it’s so universal. She was an old, lonely lady with a terrifying blunting of her once-sharp intellect, and she just wanted to talk. And maybe she was also trying to do what mothers and grandmothers do: prepare us for her absence.