Surah Ar-Rum, Ayah 54

O people! Allah is the one who created you from a despised fluid, then He gave you the strength of manhood after the weakness of childhood, then gave you the weakness of old age after the strength of manhood. Allah creates whatever He wishes i.e. strength and weakness; He is he Knower of everything, nothing is hidden from Him; the Capable nothing is beyond His power and ability.

Allah is He Who created you in weakness, then gave you strength after weakness, then after strength gave (you) weakness and grey hair. He creates what He wills. And He is the All-Knowing, the All-Powerful (54)

The Different Stages of Man

Here Allah points out how man passes through different stages of creation, one phase after another. He is originally created from dust, then from a Nutfah, then from a clot, then from a lump of flesh. Then he becomes bones, then the bones are clothed with flesh, then the soul is breathed into him. Then he emerges from his mother's womb, weak and thin and powerless. Then he grows up little by little, until he becomes a child, then he reaches the stage of puberty, then he becomes a young man, which is strength after weakness. Then he starts to get older, reaching middle age, then old age and senility, weakness after strength, so he loses his resolve, power of movement and ability to fight, his hair turns grey and his characteristics, both inward and outward, begin to change. Allah says:

ثُمَّ جَعَلَ مِنْ بَعْدِ قُوَّةٍ ضَعْفًا وَشَيْبَةً ۚ يَخْلُقُ مَا يَشَاءُ ۖ

(then after strength gave (you) weakness and grey hair. He creates what He wills.) He does whatsoever He wills and controls His servants in whatever way He wants.

وَهُوَ الْعَلِيمُ الْقَدِيرُ

(And He is the All-Knowing, the All-Powerful.)