Is prayer and fasting obligatory for an elderly father, 105 years old, who has partial memory loss and no bladder control?

The ruling on your father's religious obligations differs depending on his mental presence. If he has lost his mind and memory, then purity, prayer, and fasting are not obligatory upon him. However, if he is aware, he must adhere to the religious obligations, as long as it does not cause him undue hardship.

The mentally impaired, the insane, those who have lost their memory, and the elderly who suffer from memory loss are not obligated to perform physical acts of worship such as prayer, purity, and fasting, because they are in the position of a child who cannot discern. However, financial obligations such as zakat are not waived for them and must be paid from their wealth.

If a person is sane at times and insane at other times, he must fast during the times when he is conscious and sane, and there is no fasting upon him during the times when he is insane.