the elderly or sick person who cannot fast in Ramadan, he/she is not obliged to fast.He/She should feed one poor person for each day.
Allah says (interpretation of the meaning):
Fasting for] a limited number of days. So whoever among you is ill or on a journey [during them] – then an equal number of days [are to be made up]. And upon those who are able [to fast, but with hardship] – a ransom [as substitute] of feeding a poor person [each day]. And whoever volunteers excess – it is better for him. But to fast is best for you, if you only knew.al-Baqarah 2:184
Al-Bukhari narrated that Ibn ‘Abbas said: This has not been abrogated (Mansoukh). It refers to old men and old women who are not able to fast, so they should feed a needy person for each day.