Return of the Jedi:

YODA: Hmm. That face you make. Look I so old to young eyes?

Luke is sitting in a corner of the cramped space and, indeed, his look has been woeful. Caught, he tries to hide it.

LUKE: No... of course not.

YODA (tickled, chuckles): I do, yes, I do! Sick have I become. Old and weak. (Points a crooked finger) When nine hundred years old you reach, look as good you will not. Hmm?