When our daughter, Darrah, left for college four years ago, I knew only that I'd miss her. I imagined a certain hollowness and stillness invading our house, a pall that I'd ward off with my usual defenses: writing more articles, digging more perennial beds, engaging in all manner of compensatory bustling. I've bustled plenty, but I understand now that it's only a cover for a more surprising development. In my daughter's absence, I've begun to feel both younger and older than I had before, a tipsy state of being that I find humbling, exhilarating, and occasionally just plain weird.

Looking back, I think my shift into empty-nest status was like a cage door swinging open for a zoo animal—I didn't immediately realize I was free. Let me be clear: I love being Darrah's mother. She's an exuberant presence, full of warmth, goofy humor, and sudden, stunning insights. She's also our only child. Nonetheless, within a few weeks of her departure, I found myself taking bigger, longer strides and standing a little taller, like a plant reaching for the sun. This sense of sprouting felt familiar, but it took me a little while to place it. It was the bodily experience of youth.

When I say "youth," I'm not talking about the hormone-buzzed, bouncing-off-walls state of adolescence. I'm referring to the way I felt as a youngish adult, before becoming a mother. Who knew that parenthood would be such a weighty business? By the time I'd hugged Darrah good-bye in the parking lot of her…