In Noah Baumbach's tartly incisive "While We're Young," aging past 40 becomes a grand exercise in denial for Josh (Ben Stiller) and Cornelia (Naomi Watts), who are determined that marriage and middle age will not slow them down. They hadn't realized they had been growing more settled in their ways, something neither wanted to admit, until they encountered the vibrantly young Jamie (Adam Driver) and Darby (Amanda Seyfried). The younger couple lay claim to the inventive, emancipated experience that Josh and Cornelia now crave. Like a feast for the starving, Josh, a documentary filmmaker who's lost his edge, and his wife, Cornelia, lap up the experience of being young again, no matter how exhausting or vacuous it turns out to be. Between all their wishing and hoping to reclaim what they were, Baumbach weaves a mighty story of self-realization, the kind that comes with not merely accepting maturity but also embracing it. This remarkable film is poignant, charming and illuminating in delightfully grown-up ways.