The opening moments of every Star Wars movie tells us that the events of the film took place "a long time ago," but just how long ago are we talking? Can we use science to pinpoint when the Star Wars movies took place? If the films did take place in a galaxy far, far, away, but one that is still within our universe, then we can use the laws of physics to at least come up with a ballpark figure. Apparently, the Star Wars movies couldn't have taken place much earlier than about 4.7 billion years ago.
While that seems like a pretty wide time period still left and open, and yeah, it is, it still eliminates about 9 billion years of the universe's existence. The reason the movies couldn't have taken place that far back, is that, quite simply, it took an awfully long time after the Big Bang for all the necessary things to occur that could lead to what we see in the films. Not, the technology, but the multicellular life and the fully formed solar systems. The break down is done by Patrick Johnson, the author of The Physics of Star Wars (via Wired). The first galaxies formed a billion years after the Big Bang, It took about 5 billion years for the solar system to come into being with mature planets, and another 3 billion years for single cell life forms to evolve into something resembling creatures.
It is possible that life could have evolved in the Star Wars galaxy faster than our own. The first stages took place by random chance after all, and as such could have happened sooner in another galaxy. Still, when Star Wars says it happened "a long time ago" they could be talking in the billions of years.
Of course, all that supposes that Star Wars takes place in our universe in the first place. the author also suggests that Star Wars could be happening in a parallel universe, many of the elements that exist in Star Wars have yet to be found here, which means that they are either heavier elements that we simply haven't found yet, or that they don't exist here, which would imply a parallel universe. It's even possible that Star Wars could even pre-date the Big Bang. Measuring time prior to the Big Bang is impossible since we can't even be sure that physics worked the same way then.
Applying science to a film series where space priests can move objects with the brains may seem a little unnecessary, but then, that's the fun of being a fan of something, digging into the details and playing with them in new and interesting ways. Perhaps we'll get some more clues as to the age of the galaxy in Star Wars: The Last Jedi.