Athanasius of Alexandria
Alban Butler, writes on the subject: "Five months after this great Council, Nicae, St Alexander lying on his death-bed, recommended to his clergy and people the choice of Athanasius for his successor, thrice repeating his name. In consequence of his recommendation, the bishops of all Egypt assembled at Alexandria, and finding the people and clergy unanimous in their choice of Athanasius for patriarch, they confirmed the election about the middle of year 326. He seems, then, to have been about thirty years of age. " 

Q: How old was Athanasius when he was chosen as Patriarch?
thirty years