Apparently, dating cave paintings is quite difficult; carbon dating requires the destruction of at least some of the painting and can give quite a range. Also many paintings use pigments that don't contain carbon.
Sometimes bones, fires and other signs of human habitation are found in the caves that can also be dated but you then have to assume that those inhabitants also made the paintings.
They also use uranium dating as sometimes calcite forms over or under the painting. (The beginnings of stalagmites). QI