The church fathers also unanimously teach it:
Six thousand years of our world are not yet completed.
St. Jerome, Doctor of the Church, Commentariorum in Epistulam Pauli Apostoli ad Titum Liber Unus, I,Ib-4.
> Six thousand years of our world are not yet completed.
Council of Trullo, canon 3,
>Especially as the fault of ignorance has reached no small number of men, we decree, that those who are involved in a second marriage, and have been slaves to sin up to the fifteenth of the past month of January, in the past fourth Indiction, the 6109th year, and have not resolved to repent of it, be subjected to canonical deposition…
The Acts of the Second Council of Nicaea (AD 787), Sess. 6:
>“In the year 5501 Christ our God came to mankind and lived with us for thirty-three years and a little less than five months.”
St. Basil the Great (c. 330–379):
>"And if anyone were to say that the days mentioned in the account are not to be understood as days, he would be admitting that the sacred Scriptures are not true. For they would be saying that there were no six days, but only a confused time… the evening and the morning were the first day."
Source: Hexaemeron, Homily 1, trans. Blomfield Jackson (The Macmillan Company, 1895), p. 23.
St. John Chrysostom (c. 349–407):
>"In the first place, He [God] created light, and then darkness; He divided the light from the darkness, calling the light 'day,' and the darkness He called 'night.' And the evening and the morning were the first day… This, then, is the meaning of the expression, ‘and the evening and the morning were the first day.’ He made a day as we understand it today, with an evening and a morning."
Source: Homily on Genesis, Homily 1, trans. Roy J. Deferrari (Catholic University of America Press, 1951), p. 21.*
St. Ephraim the Syrian (c. 306–373):
>"On the first day He made the heavens and the earth, and on the second day He made the firmament, and the evening and the morning were the second day. Thus, He made the days, as we know them, with evening and morning."
Source: Commentary on Genesis, trans. Edward G. Clarke (Fathers of the Church Series, 2010), p. 87.
St. Gregory of Nyssa (c. 335–395):
Quote:
>"The days in which the creation was completed are not merely periods of time, but true days. And on the seventh day, God rested, not because He was weary, but because He had completed the work."
Source: The Hexaemeron, trans. D.H. Williams (Catholic University of America Press, 2000), p. 79.
St. Ambrose (c. 340–397):
>"The world was formed in six days. We must not suppose that the days mentioned in the creation account are mere allegories or figures of speech. It is plain that the world was created in six days and that each of these days represents a real, distinct period."
Source: Exameron, trans. H.T. Armstrong (Fathers of the Church Series, 1957), p. 67.
St. Irenaeus of Lyons (c. 130–202):
>"For in six days the Lord made all things, and rested on the seventh day from all His works, and sanctified it. Thus, the Scripture, by showing that the world was made in six days, teaches us that this number is fixed, for it is the first and the seventh which are named, and the rest of the days are set in between."
Source: Against Heresies, Book 5, Chapter 23, trans. John Keble (The Christendom Press, 1995), p. 552.
St. Cyril of Jerusalem (c. 313–386):
> "The creation of the world, the heavens, and the earth, and all that is in them, was accomplished by God in six days. On the seventh day He rested from His works, not because He needed rest, but to teach us that we should rest."
Source: Catechetical Lectures, Lecture 5, trans. A. J. Mason (Nicene and Post-Nicene Fathers, Vol. 7, 1893), p. 25.*