Shaikhul-Islam Ibn Bāz (rahimahullāh) stated:
The scholars differed over this issue. Some set the limit at fifty years, and others at sixty years. However, there is no proof for these positions, except what is reported from ʿĀ’ishah (رضي الله عنها) that she said: “A woman does not find anything in her womb after fifty.” And this was from her own ijtihād.
The correct view is that if menstruation continues for her and does not change, even after fifty, then she should continue to treat it as menstruation, because there is no evidence specifying a fixed age limit.
However, if her bleeding becomes irregular after the age of fifty and its condition changes, this is a sign that the monthly cycle has ceased and that it is no longer menstruation.
So if it becomes irregular after the age of fifty, it is not regarded as menses. This irregularity itself is from the indications of its ending: sometimes it is red, sometimes yellow, sometimes like this or that; sometimes it increases, and sometimes it decreases; sometimes it comes, and sometimes it does not.
Meaning: it becomes irregular—one month it comes and the next it does not; one month five days, another month ten, another month eight—after fifty.
Sometimes it is black, sometimes red, sometimes something else; it keeps changing.
This is clear evidence that its matter has ended, so it is not to be considered. Instead, it is treated as corrupt blood, like istihādah.
She prays while it is present, she fasts, she takes precautions by using cotton pads and the like; and she performs wudū for the time of every prayer as long as the blood remains with her—and this is if it becomes irregular and corrupted after the age of fifty.
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