Tafsir of Ya seen 36:68

(And he whom We grant long life - We reverse him in creation) i.e., We extend his lifespan, (We reverse him in creation) meaning We invert him therein, so he continues to increase in weakness and the decline of his physical structure and faculties, contrary to how he was at the beginning of his life. In this is a comparison of the metaphorical reversal to the physical reversal, and the metaphorical use of the physical term for it. It is reported from Sufyan that this reversal occurs at the age of eighty, but the truth is that the time when weakness and the decline of one's physical structure begin varies due to the differences in temperaments and circumstances, as is not hidden. This statement is a conjunction to His saying: (And if We willed, We could have blinded...), a conjunction of the cause to the effect, because it is like a witness to that.

A group among the seven reciters read (nunakkisu-hu) with a lightened tashdid (i.e., nunkisu-hu) derived from al-inkas (to invert).

(Do they not then use reason?) i.e., do they not see this and thus use reason to understand that He who has the power to do this has the power to do what was mentioned regarding blinding and metamorphosis, and that the reason these have not occurred is because His Will has not attached to them.

Nafi’, Ibn Dhakwan, and Abu ‘Amr, in a narration by ‘Ayyash, read it as (ta‘qilun) with the ta (the letter 'T') indicating the second-person address, due to the preceding discourse being in the second person.