There is a difference between a person who is unable to perform Hajj due to old age and a person who is unable due to illness, because a person who is unable due to old age cannot regain youth and strength, whereas a sick person can recover by the command and mercy of Allah Almighty.

Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrates that Sayyiduna Fadl bin Abbas (may Allah be pleased with them both) was riding behind the Messenger of Allah (peace and blessings be upon him) when a woman from the tribe of Khath’am came to ask the Prophet a question. Sayyiduna Fadl bin Abbas (may Allah be pleased with them both) began to look at her and she also started looking at Sayyiduna Fadl bin Abbas (may Allah be pleased with them both), so the Messenger of Allah (peace and blessings be upon him) turned the face of Sayyiduna Fadl bin Abbas (may Allah be pleased with them both) to the other side with his blessed hand. She said,“O Messenger of Allah, Allah has made Hajj obligatory upon His servants, but my elderly father is not able to sit firmly on a mount. Should I perform Hajj on his behalf?”The Prophet (peace and blessings be upon him) replied,“Yes.”And this incident took place during the Farewell Pilgrimage.