The first claim, that the ancient Jewish leaders understood the creation account to be allegorical, relies on extremely weak evidence. According to the Jewish Virtual Library, “The vast majority of classical Rabbis hold that God created the world close to 6,000 years ago.” Of course, this site goes on to say that “A small minority of classical rabbis believed that the world is older,” but they support this claim with a very suspicious example.
The very first example given was that “Talmud Chaggiga 13b-14a states that there were 974 generations before God created Adam.” This is a reference to a section of the Talmud which has nothing to do with the creation account in Genesis 1, but it is claimed over and over again on old earth creationist blogs as evidence that the ancient Jews did not view Genesis 1 as demanding a literal six day creation. Here is the actual text from the Talmud which mentions these 974 generations:
There is a Baraitha to the effect that R. Simeon the Holy said, These are nine hundred and seventy-four generations, which were held back from being created before the world was created, and so were not created. The Holy One, blessed be He, stood and scattered them through all the successive generations, and these are the shameless who are in a generation.
As you can see, even if we were to take this quote out of the context in which it is found and place it in the context of Genesis 1, it still would not support the old earth claim. According to this quote, the 974 generations “were not created” before Adam. Rather, they were placed within all the generations which came after Adam. To claim that this is an example of ancient Jews rejecting the literal six day creation account, one would have to do exactly what the Jewish Virtual Library did and not provide an actual quote of the passage.
This is typical of those who claim that the ancient Jews did not accept a literal six day creation account. I have never seen this claim accompanied by extensive citations of ancient Jewish authors who explicitly argued in favor of this view. Instead, the supporting references are always few, and those few are always cryptic. In reality, the ancient Jewish scholars held to a unanimous (or at least nearly unanimous) view of the young age of the earth.