I would like to know what day-age theorists do with what God says at the end of creation - that everything was "very good" (Genesis 1:31)? That is to say, if you look at the fossil record, you see death, disease, cancer, killing, etc. So how could God say at the end of creation that everything that He had made was very good?
The best way for me to answer this as a Day Age person is to quote from my main go to guy on the topic, Hugh Ross so I'm going to quote from one of his articles.
If you read the full article you will notice that Ross shows that the Bible uses the words Good and very good in both a moral sense, as well as in the sense of beauty and aesthetics.
Interpreting tob in Genesis 1 Tob carries both a moral and a physical appraisal in Genesis 1—the former based on supplementary information in Genesis 3, and the latter on the verb "saw." Hence the essential question is how to weigh these two components: is the meaning more moral than physical, or the reverse? Those who believe that the moral component dominates will typically suggest that God's creation contained not only no real evil, but also no apparent evil. Such interpreters usually picture the original creation as being like the popular concept of "Nirvana"—with no vertebrate animal death or harsh conditions whatsoever. There are, however, severe problems with this interpretation, detailed in our previous TNRTB, "What Does a 'Very Good' World Look Like?" (see here and here.) On the other hand, a strong argument can be made that the good God sees in Genesis 1 refers to the aesthetic and/or functional beauty of His creation. This is not to deny the moral aspect of the word tob in Genesis 1, but to emphasize the pleasing sight that God beheld in His work. There is harmony and structure in the creation narrative that points to the harmony and structure of the cosmos. Furthermore, His laws of nature are working together, and something that works harmoniously is beautiful to behold. Additionally, God may have seen Earth as tob because of its potential as humanity's habitat and the place where humans fellowship with the Creator.
Our belief is that the language of Genesis 1 fits better with the aesthetic/functional interpretation. Although it is true that no real evil was present in the original creation, that is not the primary emphasis. Instead, the primary emphasis rests on the beauty of the created order. This is in harmony with the language and biblical theology (Psa. 104; Rev. 4:11). By contrast, there seems little justification for those who claim there is no apparent evil in the created order. If we combine the aesthetic and functional concepts of beauty with the moral, one can see why God sees His creation as very good.
Day-age Theology does not deny the Genesis account; only that a day in Genesis does not necessarily refer to a 24 hour period. I am one. I base my belief on Genesis 1:1 as compared to Genesis 1:3 and 1:5.
Genesis 1:1 KJV In the beginning God created the heaven and the earth.
Genesis 1:3 And God said, Let there be light: and there was light.
Genesis 1:5 And God called the light Day, and the darkness he called Night. And the evening and the morning were the first day.
There is no way to determine the length of verse one until verse 3. Accordingly in my estimation time began when God said let there be light. Verse 5 says that the evening and the morning made up the first day, which appears to include the first verse in composition of the first day. Logically we would seem to deduce that verse one would be the eternity before verse 3, since the period before light would extend throughout the eternity before the creation of light.
To answer your question about dealing with the statement that "It was very good" we affirm that since at that time according to the Genesis account there was no death. If there was no death there would be no Fossils therefore the Fossil record is not broached.
It is also necessary to accept another Genesis concept that being that if there was no death there would also be no diseases and such that do lead to death; and along with that the concept that there were no Carnivores before no injuries from being killed.
We are also stymied by verses 14 through 16:
Genesis 1:14 And God said, Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs, and for seasons, and for days, and years:
Genesis 1:15 And let them be for lights in the firmament of the heaven to give light upon the earth: and it was so.
Genesis 1:16 And God made two great lights; the greater light to rule the day, and the lesser light to rule the night: he made the stars also.
Since the 24 hour day is based on the rotation of the Earth through its darkness and light, would that measurement also apply to the period before creation of the sun, moon, and Stars; after verse 3?
Comparing these verses I find there is room to question whether the Genesis account expounds a 24 hour day or not. while it is true that the Earths rotation is almost a constant 24 hour cycle; it is also clear that not always did the occupants of the Earth account for the extra time that the rotation actually takes. That alone makes a day something other than 24 hours, and if the age of the Earth is quantify 6,000 plus or minus years old do those deny the age as computed by Biblical aging?
In short what we as day-age theorist believe is that there is no conflict between the Bible and true Science, and in the end one verifies the other. at any rate if we believe that God is in fact the Creator of all things he would not create a World of imperfection, and as the Bible delineates it was man and not God who caused imperfection.