There are different Christian Interpretations of the age of the earth. Some say the earth is 7- 10,000 years old. Some say the earth is billions of years old. If I am going to make a logical assumption, I'd guess the earth is in the billions. If I am going strictly by faith, then it's a bit tougher, but still not impossible to come up with a number in the billions. If you notice, the first verse of Genesis says this:
Gen 1:1 ¶ In the beginning God created the heavens and the earth.
That whole 'in the beginning' thing is open to interpretation. There is no morning and evening assigned to this particular creative act. Therefore, I am not certain how long the earth existed before God created the 'light'.
