Contrary to popular belief, not all ancient cave art was created by senior male shamans. R. Dale Guthrie, author of The Nature of Paleolithic Art, reveals that many graphic scenes of sex and hunting were drawn by teenage male "graffiti artists." In an interview with LiveScience, Guthrie said, "Lots of the wild animals in the caves have spears in them and blood coming out of their mouths and everything that a hunter would be familiar with. These were the Ferraris and football games of their time. They painted what was on their minds." The LiveScience feature on Guthrie, which is accompanied by four cave images, can be read here.
You can also read more about Guthrie’s discoveries in this excerpt from his book.