Ibn ‘Umar said

I was brought before Allah's Messenger ﷺ in the year of Uhud when I was fourteen and he sent me back. Then I was brought before him in the year of the Trench when I was fifteen and he gave me permission to fight.* ‘Umar b. ‘Abd al-‘Aziz said this represents the difference between fighting men and children. * Ajazani. It may be translated as above or it may mean “he gave me a fighting man's permission”. (Bukhari and Muslim.)