[boanuatiguali]

أعوذ بالله من الشيطان الرجيم
بسم الله الرحمن الرحيم

A`ūdhu billāhi min ash-shaitāni r-rajīm
b-ismi-llāhi r-raḥmāni r-raḥīm



Yusuf Al-Qaradawi in In The Lawful and The Prohibited In Islam states:
By "the elderly among women" is meant such post-menopausal women as have no desire for marriage or sex, and to whom men are not attracted. Allah has made this concession for them so that they can put aside their covering garments, such as the chaddor, abaya, burqa, jilbab, and the like. However, the Qur'an makes the condition that this should not be for the purpose of displaying their adornment but only for ease and comfort. Despite this concession, it is preferable and better for them to be more perfect in their dignity and far removed from any suspicion: "but it is better for them to be modest." (24:60) [emphasis added]

Commentary on this verse (Surah An-Noor, verse 60) in Ma'ariful Qur'an is as follows:

... the third exemption is granted on the basis of a woman's personal situation. If a woman has grown so old that no one would have any (sexual) desire towards her, nor is she marriageable, for such a woman concession in hijab is allowed in that even strangers (non-Mahrams) are treated like mahrams for her. She is not required to cover those parts of her body before non-Mahrams which are not required to be covered before mahrams. Hence, it is said [arabic] (And those old women who have no hope for marriage - 60). The explanation of this verse is already given above. Although very old women are allowed to uncover those parts of their body before non-Mahrams which are not required to be covered before mahrams, yet this exemption is allowed with the condition that they do so without applying any makeup or adornment. The other thing said in the last is [arabic] (60) that is, it is better for them if they avoid going before non-Mahrams altogether. [emphasis added]

That said...

I would imagine that a woman who has covered herself her entire life would feel very uncomfortable removing her covering in old age. That said, it could be that she need not become uncomfortable if, for example, she is at home and a non-mahram comes - she doesn't need to scramble to properly secure her hijab, nor does she need to feel incompetent or distraught at not being able to do so properly... To me, this speaks of Allah's (SWT) mercy, the emphasis being ease and comfort in real old and an opportunity for us all to practice mercy towards the elderly. And Allah (SWT) is All-Hearing, All-Knowing.