In my headcanon, the Sumerian Sage is the legendary Gilgamesh, and his adventure with Enkidu would be a rivalry turned into friendship that would end when an Apple of Eden erases Enkidu's memory and the two must separate. Gilgamesh would be the embodiment of Templar ideals and Enkidu the opposite and they must stop one of Juno's tricks in ancient times.
Why not just have the actual sage in the myth be the sage in your headcanon though? Like nothing else in what you wrote needs for Gilgamesh to be a Sage for that narrative. Seems irrelevant.
