The narrations on this subject which have been reported by both Shiah and Sunni traditionalists is more than 318 traditions. Having said that, it is important to state that the Mahdi of Islam is not the only person in history who has been blessed with a long life. In fact there are dozens of other examples which are available in history of people who have had a long life. For the benefit of my Muslim brethren, just one example is quoted below from the Holy Quran,
وَلَقَدْ
أَرْسَلْنَا
نُوحًا
إِلَى
قَوْمِهِ
فَلَبِثَ
فِيهِمْ
أَلْفَ
سَنَةٍ
إِلَّا
خَمْسِينَ
عَامًا
"And surely We sent Nuh to his people, and he tarried among them a thousand years less fifty"
(Surah Ankabut, verse 14)
As per the above verse, Hazrat Nuh (as) lived amongst his people for 900 years. Traditions under this verse clearly indicate that the life of Hazrat Nuh (as) was more than 2,500 years. In fact as per the tradition of Imam Sadiq (as), Allah granted a long life to Hazrat Nuh (as) so that it would be a conclusive proof for the long life of the Mahdi.
Some of the historians who have reported traditions about the long life of the Mahdi are given below:
1. Muntakhabul Asar, chapter 30, part 20, page 276
2. Kashful Mohajjah, part 79
3. Tazkeratul Khawas by Sibt Ibne Jawzi, page 377
4. Al Bayan Fee Akhbaare' Sahebaz Zaman, chapter 25
5. Al Mo'amaroon (entire book is on this topic)
6. Tafseerul Jawaher, volume 17, page 224
7. Izharul Haqq, volume 2, page 124
8. Mahdi Mau'ood Ala Rawani, page 585
9. Al Imam Al Mahdi Menal Mahde Ilaz Zohoor, page 353
10. Tarikhe Mo'rajuz Zahab by Masoodi, volume 1, 2
11. Isbatul Wasiyyah by Masoodi
12. Daad Gustare' Jahan, page 302
13. Kamaluddin, volume 2, chapter 52, page 549
14. Chehrae' Darakshane' Imame' Zaman (as), page 268
15. Ghabate' Tusi, page 81
16. Yaumul Khalaas, page 164
17. Kashful Ghummah, volume 3, page 333
18. Beharul Anwar, volume 51, page 263