YOUR SIXTH QUESTION
What was the wisdom in his prophethood commencing when he was forty years of age, which is reckoned to be the age of perfect maturity, and his blessed life continuing for sixty-three years?

The Answer:
There were numerous purposes and instances of wisdom in this. One of them is as follows: prophethood is a great and extremely heavy responsibility. It may be borne through the unfolding of the intellectual abilities and capacity of the heart, and through their being perfected. The time they are most perfectly developed is the age of forty. In addition, youth, the time the passions of the soul are enflamed, and the blood fiery and exuberant, and worldly ambitions are intense, is not fitting for the duties of prophethood, which are purely Divine, sacred, and pertain to the hereafter. However serious and sincere a man is before the age of forty, the suspicion that he is working for worldly renown might occur to those who themselves seek fame. He could not easily be saved from their accusations. But after the age of forty, the descent to the grave begins, and the hereafter looms larger for such a man than this world. He can be easily saved from such accusations in his actions and works, which look to the hereafter, and he is successful. And others too are saved from thinking ill of him.

When it comes to his blessed life being sixty-three years, one of the instances of wisdom in it was this: the believers are charged by the Shari'a to love and respect God's Most Noble Messenger (Upon whom be blessings and peace) to the greatest degree, to feel disgust at absolutely nothing about him, and to see every aspect of him as good. Thus, Almighty God did not leave His Noble Beloved in the difficult and troublesome years of old age after sixty-three; He rather sent him to the Sublime Court at that age, which was the average life expectancy of most of the community of which he was the leader. He took him to Himself, showing that he was the leader in every respect.

The Letters / The Twenty-Third Letter