“Liberal Arts” — written by, directed by and starring Josh Radnor — is that rarity: a contemporary comedy about maturity. It’s a wise, warm tale of an adult coming of age in his mid-30s.

Radnor plays Jesse, a Manhattan university admissions counselor who returns to his leafy, idyllic Ohio alma mater to attend a retirement dinner for favorite English professor Peter Hoburg (Richard Jenkins). “Nobody feels like an adult,” says a weary Hoburg, who’s not sure he wants to retire. “It’s the world’s dirty secret.”

Jesse, who finds himself hanging around campus long after the dinner, is drawn to the idea of starting over again as a college student — or, perhaps, with a college student. Enter Zibby (Elizabeth Olsen), a sunny, ever-skipping but wise-beyond-her-years 19-year-old who’s charmed by Jesse; like Joyce’s Molly Bloom (this movie’s haunted by literature majors), she keeps on saying “yes.” A nervous Jesse — who calculates that when he was 19, she was 3 — retreats into an old-school, handwritten correspondence with her; they discuss books, classical music and life itself. Should he ditch New York and reboot with Zibby? Or can you really not go home again?

For anyone who looks back affectionately at college years — the time, says Jesse, of “the feeling that anything’s possible, of infinite choices ahead of you” — “Liberal Arts” is a smart, snappy pleasure. Radnor and Olsen banter irresistibly; Jenkins is perfect as a prickly prof afraid of the blank page of retirement; and a hilariously arch Allison Janney, as a fellow faculty member, puts the best cranky spin on the one-word line “And?” that you’ll ever hear. (If this movie were an enchilada, she’d be the hot sauce.) Radnor, who previously wrote and directed “happythankyoumoreplease” (but is perhaps best known for starring in TV’s “How I Met Your Mother”), finds both wit and truth in his characters as they face, in their different ways, growing up.

“I think being old is OK,” Jesse finally concludes. “It’s getting there that kicks your ass.”