The Qur’an mentions that Prophet Issa (peace be upon him) would see the age of maturity:
[Qur’an 3:46] “He shall speak to the people in childhood and in maturity (kahlan). And he shall be (of the company) of the righteous.”
[Qur’an 5:110] Then will Allah say: “O Issa the son of Mary! Recount My favor to thee and to thy mother. Behold! I strengthened thee with the holy spirit, so that thou didst speak to the people in childhood and in maturity (kahlan).
Scholars agree that the Kahlan is somewhere between 30 and 50. The age of maturity has been mentioned in the Qur’an as well.
“We have enjoined on man kindness to his parents: In pain did his mother bear him, and in pain did she give him birth. The carrying of the (child) to his weaning is (a period of) thirty months. At length, when he reaches the age of full strength and attains forty years, he says, ‘O my Lord! Grant me that I may be grateful for Thy favor which Thou has bestowed upon me, and upon both my parents, and that I may work righteousness such as Thou mayest approve; and be gracious to me in my issue. Truly have I turned to Thee and truly do I bow (to Thee) in Islam.’” (The Noble Qur’an, 46:15)
It is an accepted fact that Prophet Issa (peace be upon him) was 33 years and six months when Allah raised him up before crucifixion. Christians however debate his age. What is important to note is that when Prophet Issa (peace be upon him) would return, he would not become the leader immediately. He would become the leader of the Muslims after the death of Mahdi (after seven years of his emergence). This way, Prophet Issa (peace be upon him) would be 40 years old when he would become the leader of the whole world. Forty years is the age when Prophet Muhammad (may upon him be mercy of Allah and peace) received revelation and it is the age of maturity as mentioned in the Qur’an as well.
Harun Yahya states:
Close study of the relevant verses easily shows how right Islamic scholars are on this question. For example, this expression is used only with regard to Issa. Although all of the Prophets spoke with their people, invited them to religion, and communicated their message at a mature age, the Qur’an does not use such expressions when talking about them. Rather, they are used only to voice a miraculous situation, because the expressions “in the cradle” and “when fully grown,” when used one after the other, refer to two miraculous events.