I'm not sure if you were going for anatomical correctness or not. Even if you weren't, there are definitely some things that look sort of off, even with the exagerration. Here's an edit, to show what a more anatomical face would look like.

Nose oddly shaded--checked a ref
Nose too big, even for an old man--trimmed it
Lips too sausagey--puckered them a bit
Chin massive--more trimming
Forehead too short--elongated it and shaped out the skull
Eyes too high--brought them down
Perspective issues with the nose (appears to be facing outward)--cleaned that up
Yellow too bright--toned it down a tad, then added white.
I personally wouldn't totally match my edit, since who needs realism? Still, try to distinguish which anatomical changes were from intention and which were from habit.
