Caveman's era (2 wds.) (8)
![Ross](/clue/static/ross-mug.min.png)
(Other definitions for stone age that I've seen before include "Primitive period" , "25 [ERA]" , "before copper came in" , "Prehistoric period" , "Early epoch when man used pre-metal tools" .)
(Another definition for stoneage that I've seen is " long, long ago".)