An-Naḥl: 70
{ إلى أرذل العمر }
To the lowest, most contemptible stage of life. It is seventy-five years according to Ali (may Allah be pleased with him), and ninety years according to Qatadah; for there is no age in a worse state than the age of decrepitude.
{ لكيلا يعلم من بعد علم شيئاً }
So that he may return to a state resembling childhood in forgetfulness; that he might know a thing and then quickly forget it, such that he does not know it if asked about it.
It is also said: So that he does not comprehend anything after his initial intellect.
It is also said: So that he does not acquire any knowledge beyond what he already knew.
{ والله فضل بعضكم على بعض في الرزق فما الذين فضلوا برادي رزقهم على ما ملكت أيمانهم فهم فيه سواء أفبنعمة الله يجحدون }