My 91 year old dads pupils are pinpoint they don't even dialate. what could that mean?

Possibly age: Older folks tend to have smaller pupils, and if they have been small for a long time, dilation might not be evident on a casual examination. He might also have had cataract surgery which can narrow the pupils. He might also be on a drug which can make them smaller if he has glaucoma. If his vision is fine, this is not worrisome.

Parasympathetic: Overdrive. This means that the control mechanisms of the autonomic (automatic) nervous system are unbalanced. Drugs e.g. Morphine can do this or it might just be his age.