Heinlein's complicated, with regard to sex as well as everything else. To me it seems as if he underwent one and maybe two abrupt changes in style over the course of his career, but it may just have been because editors were less willing to edit him as he became famous.

In some ways Heinlein was actually ahead of his time in depicting female characters, in that he was willing relatively early on to write the hypercompetent female action superhero of the sort we've been seeing so often over the past few years. But it was usually tempered by something of the traditional gender-role notion of the time—that disappointing ending to "The Menace from Earth," just to take the most famous example.

And later on, his obsessive fantasies about being serviced by sexy, sassy girl-women in his dotage just completely took over, and there was nobody there to give it the red pencil.