Reference: http://mufti.af.org.sa/ar/content/حكم-صيام-فاقد-الذاكرة
Question: An elderly man who has lost his memory, has suffered a stroke and lost his sense of touch; so is he required to fast or not?
Response: The one who has lost his memory due to old age, and has lost all sensation and does not pray because he is unable to do so, then he is not to fast, and nor is he required to feed (fidyah) [anyone for the fasts he misses], and nor is anyone required to fast on his behalf [after his death – to make-up for the fasts he has missed due to his medical condition].
