For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
In the first verse of the Bible, God tells us that He created heaven and earth. Period. In one sentence, He created matter and formed this matter into the universe. How long it took before He began cultivating the earth and preparing it for life—the time between Genesis 1 verse 1 and Genesis 1 from the second verse onward—the Genesis days 1 through 6—we don't know. The Bible doesn't provide any information about that, so it could well be, and seems reasonable, that it was many billions of years, as science claims. But now, are the Genesis days literally 24-hour days?
People also use expressions like "old day," is that 24 hours? That would be sad. Let's let the Bible speak for itself, because we read that each day, from 1 through 6, comes to an end and a new day begins. This is not mentioned anywhere in the entire Bible regarding day 7, the day of rest. Logically, we should still be somewhere in the day of rest. 2 Peter 3 verse 8 also explains: for God, 1 day is like 1000 years, and 1000 years are like 1 day. (Time is relative for God, He has no beginning or end, He lets us know that He has always existed.) This would mean that the Genesis days could have lasted at least 1000 years. The Hebrew expression used for "day" in Genesis can also mean a (much) longer time or period of time than just a 24-hour day. So it's reasonable that the date of the start of creation is not even close to Adam's creation. As we count back, he would have been about 6050 years right now.