Fact: People do not stop being happy after the age of 30. Sometimes, looking at collections, you get the impression that designers assume that joie de vivre is the exclusive province of youth. It's worth noting that the French don't make this mistake, and neither does Co designer and cofounder Stephanie Danan, who was raised in Paris. The latest Co collection found Danan and partner Justin Kern exploring buoyancy, both in tone and in construction, but that didn't detract from the emphatic adultness they've cultivated in Co since it launched. There was a sporty inflection here, witnessed in pieces like the flared puffer vest in quilted jacquard or the baggy skirt in floral matelassé with an elastic waist. The collection also featured some gamine touches, like Peter Pan collars, and romantic ones, like ruffles and flounces. Danan and Kern also dipped a pinkie toe into denim, with a group of dresses and tops in indigo-dyed chambray. But all these typically youthful elements were deployed in restrained, sophisticated ways. The designers struck the right balance between ease and polish, focusing on fluid, voluminous silhouettes, but attending with care to the cut of those looks. Cases in point: the A-line shirtdress, shaped via pleats, and the collarless coat with a waterfall back. It takes real skill to make clothes this understated that nevertheless feel special. No wonder, then, that Co is blowing out the doors at Barneys and that it picked up Neiman Marcus this season. Turns out, grown-ups like to be happy in their clothes, too.