Give or take a couple of centuries.
I find it bizarre to claim that Hector, Achilles or Ulysses are fictional. I mean, there must have been a Prince of Troy on the defending side, a strong warrior and a willy one on the attacking side.
Whether they were named Hector, Achilles or Ulysses is not exactly important. That's how a petty war can be made into a myth.
Look at:
The Cattle Raid of Cooley ( The Táin Bó Chuailgne)
The Cattle raid of Cooley - Already here they demystifie lots of the stuff (
afaik) but, yeah, the origin of the conflict is obvious - Some people stole some cattle from someone else, war ensues and myths are written about it.
Seems obvious to me...