skygiants

I think you're right that middle-aged women outrank in golden-age detective novels, but I'd actually argue that twentieth-century Gothics (as distinct to murder mysteries) tend to have a lot of focus on teen-girls-as-people -- in large part because the protagonist is often a teenage or twentysomething girl, and if there's also a dead teenage or twentysomething girl involved, there's an element of identification/doubling with the present (for ex. Michaels' Ammie Come Home, in which a contemporary teen is haunted by the ghost of a dead one; Marilyn Ross' extremely bad The Locked Corridor, in which the heroine is attempting to solve her identical twin sister's murder; and, of course, Stewart's The Ivy Tree, in which doubling doubling spoilers.)