What is the ruling regarding someone who vowed to fast for an entire lifetime when he was young, and then became unable to do so due to old age?

Whoever vows obedience to God must fulfill it, as Allah Almighty says: "And let them fulfill their vows," and His saying: "They fulfill their vows."

If the vow was fasting and the vower became unable to perform it, the fasting is waived, and an expiation for breaking an oath becomes obligatory upon him.

Some scholars are of the opinion that feeding one poor person for each day is obligatory along with the expiation, as Al-Buhuti Al-Hanbali stated.