The narrator states: "Sayyiduna Abdullah bin Umar (may Allah be pleased with them both), whose kunyah was Abu Abd al-Rahman, died in Makkah after the Hajj and was buried at al-Muhassab, while some people say at Fakh. As for his age: when the Prophet (peace and blessings be upon him) permitted him to fight on the day of al-Khandaq, he was fifteen years old, and al-Khandaq took place in Shawwal of the year 4 AH, so at the time of his death he was eighty-four years old."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12978