The age at which Imam Mahdi will appear is a topic of debate and speculation within Islamic eschatology. According to a Hadith from Imam al-Hasan and Imam al-Sadiq, Imam Mahdi will appear at the age of 40. However, it is important to note that there is no proven hadith that definitively states how old Imam Mahdi will be when he appears. Some sources mention that he will be forty years old when he emerges, while others suggest that he will be related to the Family of the Prophet and will rule for about 7-8 years. The concept of Imam Mahdi is popular among Muslims, and it has been a part of the creed of Muslims for centuries. The exact age at which Imam Mahdi will appear remains a matter of interpretation and belief within Islamic tradition.