Spoilers för The Last Jedi :
The last time we see Luke with the green lightsaber, he is activating it in an effort to kill Ben Solo. He realizes the error of his ways immediately after activating it, but it is too late and Solo tries to kill him.
Med hjälp av kanonboken Bloodline , som är inställd sex år före Kraftvakten , vet vi att
Ben Solo had not yet turned to the Dark Side. However, due to the combination of the revelation that Darth Vader was his grandfather (Bloodline) and that his uncle/master may have wanted to kill him, The Last Jedi, Ben turned to the Dark Side. So to answer the question, Luke had his lightsaber as close as six years before the events of The Force Awakens, and most likely lost it during the destruction of his new Jedi order.