Heinlein analyzed in immortality text
The Fountain of Youth
is a scholarly work analyzing every cultural aspect of immortality from Gilgamesh to video games. It is... exhaustive. In the middle of its spelunking through literature, it devotes considerable attention to science fiction, notably Wells and Stapledon. There are several pages devoted to Heinlein starting on page 62, visiting Methuselah's Children, and dwelling longest on Beyond This Horizon, which the author sees as a deliberate rebuttal to the eugenics tracts of Haldane.