A great deal of modern popular culture — including just about everything pertaining to what French savants like to call le nouvel âge d’or de la comédie américaine — runs on the disavowal of maturity. The ideal consumer is a mirror image of a familiar comic archetype: a man-child sitting in his parents’ basement with his video games and his “Star Wars” figurines; a postgraduate girl and her pals treating the world as their playground. Baby boomers pursue perpetual youth into retirement. Gen-Xers hold fast to their skateboards, their Pixies T-shirts and their Beastie Boys CDs. Nobody wants to be an adult anymore, and every so often someone writes an article blaming Hollywood, attachment parenting, global capitalism or the welfare state for this catastrophe. I’ve written one or two of those myself. It’s not a bad racket, and since I’m intimately acquainted, on a professional basis, with the cinematic oeuvre of Adam Sandler, I qualify as something of an expert.

In the annals of anti-infantile cultural complaint, Susan Neiman’s new book, “Why Grow Up?,” is both exemplary and unusual. An American-born philosopher who lives in Berlin, Neiman has a pundit’s fondness for the sweeping generalization and the carefully hedged argumentative claim. “I’m not suggesting that we do without the web entirely,” she writes in one of her periodic reflections on life in the digital age, “just that we refuse to let it rule.” Elsewhere she observes that “if you spend your time in cyberspace watching something besides porn and Korean rap videos, you can gain a great deal,” a ­hypothesis I for one am eager to test.

But the present and its technological lures and discontents, thankfully, are not really her concern, any more than the jeremiad is her chosen form; she comes across as a patient pedagogue rather than an angry scold. She sprinkles in a few musical references — to Lady Gaga and the Rolling Stones — and occasional nods to unspecified “studies.” In spite of these, “Why Grow Up?” isn’t an exercise in pop-culture polemics or pop-sociological cherry-picking. It’s a case for philosophy of an admirably old-fashioned kind. Neiman is less interested in “The Catcher in the Rye” than in “The Critique of Pure Reason,” and more apt to cite Hannah ­Arendt than Lena Dunham.

Nor, in spite of its subtitle, is her book a critique of contemporary mores. The “infantile age” she has in mind goes back to the 18th century, and its most important figures are Jean-Jacques Rousseau and Immanuel Kant. “Coming of age is an Enlightenment problem,” she writes, “and nothing shows so clearly that we are the Enlightenment’s heirs” than that we understand it as a topic for argument and analysis, as opposed to something that happens to everyone in more or less the same way. Before Kant and Rousseau, Neiman suggests, Western philosophy had little to say about the life cycle of individuals. As traditional religious and political modes of authority weakened, “the right form of human development became a philosophical problem, incorporating both psychological and political questions and giving them a normative thrust.”