As a current atheist, I would like to debate them on this claim that the five books of Moses of the Pentateuch in its current form is the original text dating back to Mount Sinai in 1313 BCE. Did the current language even exist in that time? Is there specific evidence I can show them that disputes that assertion?
edit To clarify, I do not accept the claim that the torah was god given, i am trying to determine the age of the language in its current form.
Did the current language even exist in that time?
No. In the 14th century BCE, Hebrew would have been little more than various local dialects of Northwest Semitic (Canaanite). Contrary to the biblical narrative, it was not the language of foreign conquerers, but the indigenous language of the Syrians and Canaanites.
Hebrew developed into a written language around the 8th century BCE. The oldest known example of Hebrew written on papyrus is from the mid-7th century BCE. Prior to this, it was not a literary language, but was used mainly for minor inscriptions, pot markings, etc.
Practically all Old Testament scholars acknowledge that most of the Hebrew Bible (including the Torah) developed in the post-exilic period. There is no extant documentary evidence for the Torah earlier than the Dead Sea Scrolls (2nd century BCE to 1st century CE), and the earliest complete manuscripts in Hebrew are from the medieval period.
Incidentally, there are plenty of branches of Judaism that fully acknowledge the non-historical nature of the Pentateuch. David Wolpe, a conservative Jew who is considered the most influential rabbi in the US, openly acknowledges that the Torah is not literal history, that the Exodus did not happen, and so on.
You may be interested in a recent podcast on this exact subject by the AskHistorians team.
"A (Brief) Textual History of the Hebrew Bible"
/u/Husky54 [7] speaks to /u/400-Rabbits [8] about the Hebrew Bible. They cover what exactly the "Hebrew Bible" really is, when it was written, who was doing the writing, the historical precursors, corresponding epigraphy, and textual intricacies.