Just how long ago was "a long time ago?" Millennia? Aeons?
I read somewhere a long time ago that the events in Star Wars are based on the passive observations of C-3PO and R2-D2, who just happened to be there doing the jobs they do while galactic events unfolded around them. The stories we know from this time period are really historical accounts recorded by these two droids.
Based on that idea, I thought a long time ago that R2 and 3PO had been built and were in service for years prior to the Clone Wars. So the fall of the Old Republic, the tragic tale of its Jedi Knight protectors, the story of the Skywalker family, and the rise and fall of the Empire were taken from the memory banks of R2 and 3PO at the time of or after their eventual deactivation.
Alas, we learned, not such a long time ago, that Anakin Skywalker constructed the protocol droid C-3PO for his mother Shmi. And R2-D2 was just another anonymous astromech in the service of a peaceful monarch on an outlying world. So much for the romanticized view of R2 and 3PO plying the galaxy together for a millennia.
I think it would have been neat had Lucas begun Episode I with a prologue that the sheds light on the time frame of "a long time ago," or at least the sources of the historical events we bear witness on screen. I’ve never considered Star Wars to be even remotely connected with Earth, unless the films were set eons in our own future, long after humans could be found throughout the galaxy and not confined to just one planet. Of course, "in a galaxy far, far away" precludes any Earth connection to the events of Star Wars anyway.
A possible prologue to Episode I could have been set in the "present day" at an archaeological dig on some desolate planet. At the site, two rusted-out husks that we barely recognize as R2 & 3PO are unearthed. The two ancient droids are carefully recovered and removed to a field laboratory. A dusty, scruffy, bearded academic in fedora and leather jacket carefully reactivates them in an attempt to access their memory banks. Eureka! Although much of the data is corrupted or lost, enough information can be retrieved to reconstruct this ancient period of a long time ago.