“Am I acting my age now? / Am I already on the way out?” Billie Eilish croons in a beguilingly sweet tone in “Skinny,” the opener from her new album, Hit Me Hard and Soft. It’s a jarring turn in a tune that otherwise just catches us up on romantic wrinkles since her last release, 2021’s Happier Than Ever, wondering why we always conflate a petite frame with a satisfied mind. “Skinny”’s trip into the artist’s concentric layers of stress — it traces her grappling with self-love...