The Stone Age was a prehistoric period during which stone was widely used in the manufacture of implements with a sharp edge. It was followed by the Bronze Age.
The 1939 cartoon film called Daffy Duck and the Dinosaur was set in what appeared to be an anachronistic version of the Stone Age. (VOY: "Memorial")
In 2267, Lindstrom described the Beta III Lawgivers as "a bunch of Stone Age characters running around in robes". (TOS: "The Return of the Archons")
In 2365, Jean-Luc Picard commented that Humans with 24th century technology would have appeared magical to Stone Age people. (TNG: "Contagion")