Yes, it certainly can be extended back. And you can make the argument that the Greeks were the true inventors of literature, back in 10th century BC.
The argument has been made that although written Hebrew was earlier than written Greek, Greek was the first written language in which new literary texts could be widely read. The Hebrew Bible was not pointed in the early texts, so it was difficult or impossible to know how to pronounce or read it unless it was accompanied by an oral tradition of rabbis who could train up new generations to understand what it said.
With the Greek alphabet, on the other hand, you could write a new poem or a play, and anyone could pick it up, read it, and now how to pronounce it, without any oral guidance. That was the necessary prerequisite to the Greek Golden Age, and it happened centuries earlier.
Just going on what the author said, though. You would think that because he mentioned Pythagoras, he would have said 6th instead of 5th century.