At 34, Arnaud Mustier is a successful lawyer and philosopher, admired for his achievements and excellence. But to his 16-year-old brother Jules, Arnaud is mostly a pain—really, really annoying! Everything changes when Arnaud starts experiencing strange impulses and discovers a few pimples. The diagnosis: he suffers from a rare case of late-onset puberty. Swept up in a whirlwind of hormones and accompanied by his brother and their friends, Arnaud sets out to discover the youth he never had.