I've been thinking lately about Mary Hartman's husband's hat. You might remember Mary Hartman, Mary Hartman, the TV show that debuted in the late '70s. This Norman Lear satire of a soap opera showcased the strange citizens of the mythical town of Ferndale. Mary's husband, Tom, was a comparatively normal specimen, though he was naïve and boyish, hardly man enough to head a family. The audience could tell this as soon as he appeared on screen because he wore a baseball cap.Armchair anthropologists will note that the cultural meaning of a baseball cap has shifted in 20 years: it used to be the equivalent, for an adult, of a flashing sign reading I'm not serious. Today it is ubiquitous. The phenomenon of "Casual Friday Creep" is elbowing business attire out of the rest of the week and "casual" is slipping from khakis-and-loafers to jeans-and-sandals. Many grownups dress like they're headed to a play date.A corresponding shift is happening at the other end. Grammar-school girls used to wear puffed sleeves and a sash in the back. Now they wear skirts and knit tops, miniature versions of their moms' outfits.This is hardly the most pressing moral issue of our day. But the loss of separate clothing codes for children and adults is interesting, because it reveals the general loss of markers for adulthood. It used to be replacing your baseball cap with a Homburg told the world you had achieved grownup status. Now the boundary line for adulthood is less distinct.Some grownups are having trouble figuring out how to grow up, and there are reasons they might not want to. A century ago, adulthood was a proud achievement. Childhood was a time of preparation for adult life, and children were mainstreamed into that life as much as feasible. ...