Corrected entry: When Grindelwald is shown stealing the elder wand in one of the original movies, he was a much younger man that he is in "Beasts." And the battle between him and Dumbledore was much later. But he doesn't have the elder wand when impersonating Graves.
origamibob
23rd May 2017
Correction: Of course he's not using the Elder wand. If he was impersonating Graves, he would need to use Graves' wand, else questions would be raised. Grindelwald was a boy when he stole the wand from Gregorovich and then went on his reign of terror across Europe. His battle with Dumbledore didn't happen until the 40's.