When talking about the age of the Gilgamesh Epic in general, not about the age of one of its many version that have been created during many centuries, it is appropriate to refer to the earliest version, not to the much later version written in the standard Akkadian language.

As mentioned in the article, in the beginning there were 5 separate stories about various adventures of Gilgamesh, written in the Sumerian language, some time around 2200 BC to 2000 BC.

A few hundred years later (around the time of Hammurabi), some Old Babylonian writer has translated the Sumerian stories into Old Babylonian, while making various changes to them in order to make them fit into a single long epic.

The Old Babylonian writer has also written several other stories, which were interleaved between the Sumerian stories and which integrated everything into a coherent epic.

Hundreds of years later, the Old Babylonian version was modified into the standard version that is best known. That version was also modified later into various other versions, some of them being translated into various languages of the neighbors of the Akkadians.

While there are many other earlier writings that can be considered as works of literature, the 5 Sumerian stories about Gilgamesh are one of the earliest examples of writings that are of the epic kind, i.e. which describe the adventures of some fictional character.

Most of the older writings mentioned in the article are not of this kind, but they may be considered as lyric, didactic or historic.

Most stories that might be older than the 5 Sumerian stories about Gilgamesh are other Sumerian stories about their gods, most of them being stories about Inanna, as mentioned in the article.

However, the age of all these Sumerian stories is not known with certainty, just that they have been written some time in the second half of the third millennium BC.

Some of the other Sumerian stories might be even a few centuries older than the 5 Gilgamesh stories, but they might as well be of a similar age.

So when talking about the earliest literature of the epic kind, it is not possible to pinpoint which is the earliest known work, but one must give a list that contains the Sumerian stories of the 3rd millennium BC, including the 5 stories about Gilgamesh.

The Sumerian stories about Gilgamesh might be the earliest where the main hero is identified as a human, not as a god.