What is the difference between Heinleins juvenile and adult works?
Very little. Most of the so-called juveniles are read with complete satisfaction by adults, and most of the adult works are accessible and enjoyable to teens and even pre-adolescents. The primary difference is that the twelve juvenile novels and handful of stories written for Boys’ Life magazine have no explicit sexual references and somewhat simplified moral issues. There is very little reason for drawing any distinction between the two categories, especially with respect to the novels. The division is made in this FAQ only because “Heinlein’s juveniles” are a recognized sf landmark. In fact, Starship Troopers was written as a juvenile, rejected by Scribner’s, and published by Putnam as an adult novel. Podkayne of Mars was written as an adult novel but is usually classified as a juvenile because of its teenage female protagonist.