Watch Teenage Caveman for Free: How to Stream the Movie Online at 123Movies. . In a post-apocalyptic future mankind is lives in a prehistoric manner. After killing his father for sexually assaulting his girlfriend, the son of a tribal leader runs away with a group of his teenage friends. They are taken in by Neil and Judith who introduce them to the vices outlawed by their tribes namely sex and drugs.Neil and Judith, however, are genetically altered indestructible mutants who have their own plans for the future of the human race.