MaximRecoil said:

According to "Wookieepedia", the X-wing was first used at the "Battle of Turkana", the year before the events of the original Star Wars movie ("1 BBY"), after stealing X-wing prototypes at the "Battle of Fresia" (also in "1 BBY"). "Wookieepedia" also says that the X-wing remained in use for over 40 years.

I don't know where any of that information actually comes from

If you check the citation on Wookieepedia, it credits the game Empire At War, but I'm positive its origin is the older game X-Wing. Either way it's EU.