The Quran

Preface

وَوَصَّينَا الإِنسانَ بِوالِدَيهِ إِحسانًا ۖ حَمَلَتهُ أُمُّهُ كُرهًا وَوَضَعَتهُ كُرهًا ۖ وَحَملُهُ وَفِصالُهُ ثَلاثونَ شَهرًا ۚ حَتّىٰ إِذا بَلَغَ أَشُدَّهُ وَبَلَغَ أَربَعينَ سَنَةً قالَ رَبِّ أَوزِعني أَن أَشكُرَ نِعمَتَكَ الَّتي أَنعَمتَ عَلَيَّ وَعَلىٰ والِدَيَّ وَأَن أَعمَلَ صالِحًا تَرضاهُ وَأَصلِح لي في ذُرِّيَّتي ۖ إِنّي تُبتُ إِلَيكَ وَإِنّي مِنَ المُسلِمينَ

Yusuf Ali

We have enjoined on man¹ kindness to his parents: In pain did his mother bear him, and in pain did she give him birth. The carrying of the (child) to his weaning is (a period of) thirty months.² At length, when he reaches the age of full strength³ and attains forty years, he says, “O my Lord! Grant me that I may be grateful for Thy favour which Thou has bestowed upon me, and upon both my parents, and that I may work righteousness such as Thou mayest approve; and be gracious to me in my issue. Truly have I turned to Thee and truly do I bow (to Thee) in Islam.”

Cf. 29:8 and 31:14.
In 31:14 the time of weaning was stated to be at the age of two years, i.e., 24 months. See also 2:233. That leaves six months as the minimum period of human gestation after which the child is known to be viable. This is in accordance with the latest ascertained scientific facts. The average period is 280 days, or ten times the inter-menstrual period, and of course the average period of weaning is much less than 24 months.
The maximum period of breast-feeding (2 years) is again in accordance with the time that the first dentition is ordinarily completed in a human child. The lower milk incisors in the centre come out between the 6th and 9th months; then come out the milk teeth at intervals, until the canines appear. The second molars come out at about 24 months, and with them the child has a complete apparatus of milk teeth. Nature now expects him to chew and masticate and be independent of his mother’s milk completely. On the other hand it hurts the mother to feed from the breast after the child has a complete set of milk teeth. The permanent teeth begin at the sixth year, and the second molars come at 12 years. The third molars are the wisdom teeth, which may appear at 18 to 20 years, or not at all.
The age of full strength (ashudd) is held to be between 18 and 30 or 32.
Between 30 and 40 the man is in his best manhood. After that he begins to look to his growing issue, and rightly commends the new generation to God. Perhaps his spiritual faculties also gain the upper hand after 40.