Well, Ewan often wears a beard- in fact, he had to shave it off for TPM... but then he only grew it again for Litte Malcolm and the Eunuchs... and for Moulin Rogue he had to be both bearded and shaven... never mind.
As Alec Guiness had a beard this was a somewhat inevitable piece of continuity. And he DOES look older in it, to be sure!