It seems that when his uncle became Pope Pius IV, he made his young nephew Cardinal and then administrator of the see of Milan. Then he was given other offices and made papal secretary of state. He was not yet twenty-two and not yet ordained!
He assisted at the Council of Trent and helped draft the catechism. Finally, in 1563 he was ordained a priest and consecrated a Bishop. After the death of his uncle, he was allowed to return to Milan and dedicate himself to reforming the diocese. He died at the age of 46. Here is a quote from him:
"If we wish to make any progress in the service of God we must begin every day of our life with new eagerness. We must keep ourselves in the presence of God as much as possible and have no other view or end in all our actions but the divine honor."