One recent Monday morning, I was telling a co-worker about my weekend: There had been a playdate with my daughter, Sasha, and one of her friends, and I'd been having some trouble with my apartment's hot-water heater, and I'd gone shopping at the farmers' market for vegetables for the week. All in all, nothing special. Just a typical Brooklyn weekend.

But for my co-worker, this was amazing. "You're a real grown-up!" she said.

I wasn't quite sure what to say. I'm still relatively new to the working world. After freelancing for the last eight years, I've only just taken a full-time job—and it's one where I'm at least a decade older than almost everyone on my team. At the age of 38, married, with kids, a mortgage, a beard, and a receding hairline, I suppose I must really seem like an adult to them.

If only I seemed like that to myself! Though I never wanted to be one of those much-derided man-children loafing around Brooklyn coffee shops—"grups," New York magazine dubbed them—I was never all that eager to embrace the traditional outward markers of adulthood: suit and tie, office job, lightless dead eyes. And in truth, I'd always felt like a child. The sense of smallness and powerlessness that are a child's everyday experience had never fully left me. When I'd look at my own father, a tenured history professor, I could never imagine becoming like him. And when I looked at kids, I felt nothing but sympathy—I know what you're going through—and imagined they were looking at me and thinking, Dude, you look older, but I see through you; you're just like me.

Still, degree by degree, things shifted. Six years ago, I grew a beard, mostly because, clean-shaven, I looked like I was still 17 years old. I invested in some good shirts and stylish blazers—not office-drone garb, but clothes I felt comfortable in. And, of course, I got married and had kids and bought an apartment. Inside, I felt no different from before—small, nervous, new to everything—but apparently I was. Or, quite possibly, the world was different, not in its essence but in how it viewed me. My own children, for example, will never see me as anything but a grown-up, and as they age, the kids of her generation will see me that way, too. One day, my daughters may look at me as I looked at my own father, and think: How am I ever going to become that?

The secret (which is only a secret to those still too young to have experienced it) is that adulthood is not something we consciously embrace, a set of rules we one day agree to follow. It's a set of perceptions and assumptions that everyone has about us, though we may still feel like children inside. How the hell did I become an adult? It's because the young people at my office decided I was. And one day, 10 or 15 years from now, it'll happen to them, too. We all grow up, whether we want to or not.

–Matt