Perhaps evidencing there being some debate in this time as to whether Jesus could also be, by means of agency/divine investiture, be the "Ancient of Days" (and/or am ambiguity between the and an Ancient of Days), Hippolytus of Rome, in his commentary on Daniel, said that the person of God the Father is the only Ancient of Days:
11.1. And so as
many of you all who reverently draw near to God, observe the person (Or: things)
who long ago was shown to the people by
Moses and was manifested on the mountain and was proclaimed by the prophets and
was seen as a man by the blessed Daniel, concerning whom he says, “I was
looking into the vision of the night, and behold, one was coming like a son of
man with the clouds of heaven, and he reached the Ancient of Days and was
brought near to him and to him was given power and honor and the kingdom and
all peoples, tribes, and tongues served him. His authority is an eternal
authority, which shall not pass away and his kingdom shall not be destroyed.” (Daniel 7:13-14)
11.2. And so he
does not speak of another Ancient of Days (τον παλαιουντα τασ ημερας), but
indeed the Lord and God and Master of all, the Father of even Christ himself,
who is the Ancient of Days he who does not grow old under time or days,
concerning whom was spoken above, “Thrones were set and the Ancient of Days sat
and his clothes were white as snow and the hair of his head was as pure wool.
His throne was a flame of fire, its (or: his) wheels blazing fire. A river of
fire gushed (Lit: derived) from before
it. A thousand thousands attended him and myriad myriads stood before him.” (Daniel
7:9-10) (Hippolytus of Rome, Commentary
on Daniel, Book 4 [trans. T.C. Schmidt, 2010])