Teenage Caveman (1958)

Starring Robert Vaughn, Darah Marshall, Leslie Bradley, Frank DeKova, Charles Thompson
Directed by Roger Corman
(actor & director credits courtesy IMDB.com)

In a primitive society, a teenager among the cave people questions the laws to never move beyond their territory, and is tempted to break the law by another caveman looking to seize power.

Roger Corman tries his hand at a caveman picture, and in my opinion it's really one of the better ones, with an insightful script from R. Wright Campbell, and a decent performance from Vaughn, some time before his success on television.  It's also clearly a low budget affair, cobbled together with stock footage from other pictures, notably One Million B.C., and recycling a costume in a nonsensical way from Night Of The Blood Beast.  Still, the ideas in the screenplay made it work for me, Frank DeKova's antagonist was a worthy villain, and it was a great relief that the cave people all spoke English instead of the grunts and yells one has to sit through and try to make sense of in other pictures of this type.  It was also fun to spot the Corman regulars among the supporting cast, with Jonathan Haze, Barboura Morris, and Beach Dickerson all making appearances.  I won't give away the twist ending, but like that Campbell laid the groundwork for it in his story beforehand.