A very old person or a person who is very ill is unable to keep the qadha of fasts he had missed in past years.

Answer

If due to extreme old age or such illness from which there is no hope of recovery one is unable to f a s t, t h e n t h e F i d y a h (compensation) has to be paid. For one fast it is the Sadqah Fitr amount, that is, the price of 2 kg flour. This has to be given to a poor Muslim.