Firstly: The Ruling of the Fast of the Old Man and Woman
Fasting is permissible for the old man and woman who cannot bear fasting. Consensus has been quoted over this by: Ibn al-Mundhir, Ibn Hazm, and Ibn `Abd al-Barr.
Secondly: The Obligation upon the Old if They Break their Fast
If the old man or woman break their fast, then they must feed a destitute for each day they do so. This is the position of the majority: Hanafis, Shafi`is, and Hanbalis.