Surah Al-Qasas 28:14

وَلَمَّا بَلَغَ أَشُدَّهُۥ وَٱسْتَوَىٰٓ ءَاتَيْنَـٰهُ حُكْمًا وَعِلْمًا ۚ وَكَذَٰلِكَ نَجْزِى ٱلْمُحْسِنِينَ

And when he attained his full strength and was [mentally] mature, We bestowed upon him judgement and knowledge. And thus do We reward the doers of good.

Translation: Saheeh International

Tafsir

And when he came of age namely at 30 or 33 and then was fully mature that is when he reached the age of 40 We gave him judgement wisdom and knowledge comprehension of religious matters before he was sent as a prophet. And so just as We rewarded him do We reward those are virtuous to their own souls.

Excerpt from Tafsir al-Jalalayn, commentary on 28:14, via Quran.com. The reader has the full commentary and 9 more tafsirs.