Excerpt from Todd VanDerWerff's AV CLUB article on the GIRLS episode "It's A Shame About Ray":
Throughout “It’s A Shame About Ray,” characters tell other characters to “grow up,” either literally in those words or just in general. Girls is a show about people who think that being grown up requires doing things a certain way—preparing pad Thai for your friends from scratch, getting married, having a house, moving on past a broken relationship—but they’re only starting to realize that nobody quite understands what being grown up means. It’s not an achievement you can unlock. It’s a thing you keep moving toward, until you’re old and perhaps experienced and realize just how little you knew back when. Put another way: I look back at the me of 10 years ago, the me who was 22 years old, and I think, “Jesus Christ, that guy was an idiot,” but I lack the self-awareness to know that 42-year-old me will look back on this version of myself and say, “What the fuck was he thinking?” Being grown up means being perfectly self-aware, and that’s almost impossible to achieve.