The Quran

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

Ali Unal

Now (among the good deeds), We have enjoined on human is the best treatment towards his parents. His mother bore him in pain, and in pain did she give him birth. The bearing of him and suckling of him (until weaned) is thirty months.¹ When he has finally reached his full manhood² and reached forty years of age, he says: “My Lord! Arouse me that I may be thankful for all Your favors (life, health, sustenance, faith, and submission, and more) that You have bestowed on me and on my parents, and that I may do good, righteous deeds with which You will be pleased; and grant me righteous offspring (so that they treat me righteously, as I treat my parents). I have turned to You, and I am one of those who have submitted to You.”

Verse 2: 233 says that, (if they wish) mothers can suckle their children for two whole years; and verse 31: 14 expresses the same, that weaning was in two years. So when the statement that the pregnancy and nursing of a child consists of 30 months is considered together with these verses, it is understood that the shortest period of bearing a child is 6 months. That is, a mother can give birth to a healthy baby in 6 months. So if a woman gives birth at the end of the sixth month of her pregnancy, she cannot be regarded as having committed the crime of adultery.
The age of full manhood or full (physical) maturity is, in the first stage, 15-20 or so years. The middle stage is 30–33 years, and the age when one is supposed to reach full intellectual and spiritual maturity is 40 years. It is rare for people to change their belief and way of life after forty.