Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates: I was presented before the Prophet Muhammad (peace be upon him) when I was fourteen years old, but the Prophet (peace be upon him) did not permit me (to participate in battle). In the opinion of the Prophet (peace be upon him), I had not yet reached maturity. Then, when I was presented before him at the age of fifteen, the Prophet (peace be upon him) gave me permission.
Hadith Referenceصحیح ابن حبان / كتاب السير / 4728
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - انظر ما قبله.فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح على شرط الشيخين