There is reason to:
A) believe in an old age universe, and
B) believe that God created what was on the Earth in 6 24/hour cycle days.
Notice what the bible says:
"In the beginning, God created the heavens and the Earth"
---This is the first verse of the first chapter of the first book in the bible. The existence of the universe was created by God. How long did that take? Well, the existence of the heavens and the earth precedes the statement "God created the heavens and the earth" because created is used in past tense here. It could be billions of years. But notice the focus of the next verse.
"Now the earth was formless and empty, darkness was over the surface of the deep, and the Spirit of God was hovering over the waters. "
---the focus is earth, and the point of reference if right above the oceans or waters of the earth.
---From this point on, the Sun existed and the moon existed. It would be illogical to have had some expansion of the universe (either from big bang or not, but definetly from a singularity) create the mass of the earth and not that of the sun or the moon or the milky way galaxy for that matter. Look at the point of reference. God is hovering over the waters. Then he said Let there be light! And there was light. God called the light day and the dark night.
The next day, God said, "Let there be an expanse between the waters to separate water from water." So God made the expanse and separated the water under the expanse from the water above it. And it was so. God called the expanse "sky." And there was evening, and there was morning—the second day."
---Now we have a translucent atmosphere that allows light to penetere the atmosphere. That atmosphere was opaque before and would not allow sunlight to penetrate.
The next day God said "Let the water under the sky be gathered to one place, and let dry ground appear." And it was so. God called the dry ground "land," and the gathered waters he called "seas." And God saw that it was good.
Then God said, "Let the land produce vegetation: seed-bearing plants and trees on the land that bear fruit with seed in it, according to their various kinds." And it was so. The land produced vegetation: plants bearing seed according to their kinds and trees bearing fruit with seed in it according to their kinds. And God saw that it was good. And there was evening, and there was morning—the third day.
---This could only be done if plant-life could photosynthesize.
Notice what happens on day four.
God said, "Let there be lights in the expanse of the sky to separate the day from the night, and let them serve as signs to mark seasons and days and years, and let them be lights in the expanse of the sky to give light on the earth." And it was so. God made two great lights—the greater light to govern the day and the lesser light to govern the night. He also made the stars. God set them in the expanse of the sky to give light on the earth, to govern the day and the night, and to separate light from darkness. And God saw that it was good. And there was evening, and there was morning—the fourth day.
---Now the atmosphere was transparent rather than translucent. God does not have to recreate the sun, but the text stated that God in fact is the Creator of the sun and the moon and the stars. Its a statement that God created everything that is visible and now we are affected by the gravitaitonal affect the moon has on us and the effect that ultraviolet radiation have on us as a result of a transparent atmosphere.
You see, the universe took billions of years to be where it was at (including the mass of earth as protoplanet), but only a few days to make protoearth a life-sustainable.
God didnt create the heavens and the earth in seven days. He created the universe, then in a matter of a few days, made it life-sustainable.
I used to think that each day was a stage or era, but then I read a little closer into the text, its order, focus and frame of reference, and deduced that God is not illogical, as our laws of nature are not illogical, but that If I adhered to the doctrine that the Sun was created on the fourth day, then I have to place the sun and moon onto the galaxy model after the creation of the universe, and that is completely illogical. It is simpler that the sun and moon were there with the earth at the point of creation when the universe was set in motion and that the opaqueness of the atmosphere of protoearth did not allow for sunlight to penetrate the surface.