You know there is a great deal of debate on how old the earth really is. The issue at hand for Christians and skeptics alike seems to be the "tension" between what science says the age of the Earth is and what the Bible says it is.
Let me throw my two cents into the pot just to keep things stirred up!
My first thought is this - We read in Gen. 1:1-2 the following:
"In the beginning God created the heavens and the earth. 2 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."
Now my first question is raise because of verse 2. Namely, how long was the earth in this condition before verse three?
Answer: We do not know. It could be billions of years for all we know. The point is the time that lapses durring verses 1 & 2 does not effect verses 3-31. Also we do not know how much time went by before the fall.
So there is one biblical explanation for an old earth/universe. But let me throw out another explanation that I am finding to be more probable.
What if God made the earth and, in fact, the whole universe fully mature? Here is what I mean.
For example, when God made man He made them fully grown people. He did not take an egg in one hand and a sperm in another and mash them together, holding them in His hands until 40 weeks had gone by, nurtured a child, help him grow from baby to boy and from boy to man. No, He created Adam (and Eve) already fully mature creatures, past puberty and capable of producing offspring right from the start. So, even though they had the appearance of, say, a 30 year old man and woman, they in fact were actually only 1 day old as far as actual time is concerned. The same is true of the vegetation, the birds of the air, beasts of the land and the creatures of the sea.
Does it not stand to reason that when God created everything else that he did so as a fully mature Earth ready and capable of handling what God was about to put on it? That the sun was made fully mature and ready to provide the life sustaining energy the Earth would need to sustain what God was going to put on it? That the Universe itself was made fully mature and ready to handle the earth that God made and put in it?
Here is my point: While science may in fact accurately observe an old Earth, it does so based upon appearance not actual time. Meaning - while the Earth may seem old given it's mature state, in fact only about 10,000 years of actual time has elapsed. Thus, when we do carbon dating and measure the universe in light years or whatever, what we are measuring is actually the 'maturity' of the universe and not the actual amount of 'time' that has lapsed.
If we think that time and maturity are the same then we are making a huge assumtion and run the possibility of misleading our selves into thinking that the earth and the universe took billions of years to get to the point it is at now. If your view is that the two are the same, I can understand the difficulty in reconciling science with scripture.
Just some food for thought when considering Earth: young or old.