Translated for IslamQA.

All Praise is for Allah.

Scholars of Arabic language have different opinions, and the scholars of Islamic Jurisprudence followed them in this difference, about setting the limits for the age of youth. The best opinion seems to be that the period of “youth” (shabab) starts from puberty and ends at 30 or 32 years, after which the period of “kuhoolah” (middle-age) starts.

Allah knows best.