Allah is He Who created you in (a state of) weakness, then gave you strength after weakness, then after strength gave (you) weakness and grey hair. He creates what He wills. And it is He Who is the All Knowing, the All Powerful (i.e. Able to do all things).
It is Allah Who creates you and takes your souls at death; and of you there are some who are sent back to a feeble age, so that they know nothing after having known (much): for Allah is All-Knowing, All-Powerful. (Surat an-Nahl: 70)