First let me say that many sincere people believe in the Bible and also believe in an old earth. They do this via the gap theory or day age theory or some other means of interpretation.
Secondly, let me say that I am not certain about the age of the universe, the age of the earth, or when the first humans walked the earth. I have read very persuasive scientific arguments for an old earth, and have read some counterarguments that may have merit. I don't feel qualified scientifically to make the judgment.
But when I am asked what Genesis appears to be saying, it is not so vague. To me it just seems so difficult to find other positions in Genesis 1, other than the literal 24-hour days position, without importing them. Hard to see them there to export! I have read widely the Intelligent Design material and I like it. I believe it certainly serves a good purpose, but its assumption of the old universe may not be valid.
I get concerned when we accept as givens premises that seem out of tune with Scripture. Yet I also recognize people’s genuine concerns about the extreme apparent age of the earth. So I respect friends who hold to the gap theory and day age and the variants, and appreciate their insistence on inspiration. But when I listen to the proponents of these theories, I’m still left feeling it’s obvious that no one would ever have come up with such interpretations except to solve a problem. And how many problems of one era of history disappeared on their own, only to leave believers with a strange biblical interpretation the text doesn’t and never did support?
I particularly cringe when I hear evangelicals view Genesis 1-11 as poetry or allegory and talk about God using macroevolution to “create” the first man and woman, which is basically “stick a soul in a sufficiently evolved primate.” What are the implications of Jesus and his obvious belief in the first man and woman, and Paul’s explanation that we all sinned in Adam? If God created Eve out of Adam, then that is an explicit disproof of God choosing two primates to honor as the “first man and first woman.”
If Paul was wrong, then so much for inspiration. If Jesus was wrong, so much for salvation. Yet, I know evangelicals, including some bestselling authors and prominent influencers—who though they avoid saying these things publicly—nonetheless, believe them privately, or at least consider then viable positions. But without the biblical doctrine of creation, there is no doctrine of redemption.
Speaking of this subject, I'm presently leading a group of mostly younger men in a study of creation, using two books: Schaeffer’s Genesis in Space and Time and Lee Strobel’s The Case for a Creator, which contains interviews with a number of the major Intelligent Design proponents (and assumes an old earth, not a young one). They're both great books, which I would encourage you to pick up from your local Christian bookstore.