The age of the Earth has been calculated to 4.54 ± 0.05 billion years, which is only approximately a 1% uncertainty. Now the exact numbers may be refined slightly as more detailed investigations are completed, there is now so much data backing up a 4.5 billion year age, that the chances of it being substantially inaccurate are very low.
This age has been confirmed by analysis of zircons in minerals, radiometric dating using a variety of elements and methods both with Earth rocks, lunar rocks and asteroid material. It has further been verified by conclusions from the field of stellar evolution (helioseismic dating), which all confirm an age of approx. 4.5 billion years, both for the Earth and for the solar system in general.
If you are religious and you believe God created earth, then you have the Christian calandar to go by. Still, when did God begin? It is said he just "was" and always is. How can you put a time or date on that? If you believe the scientific idea, the the earth has been here for millions of years.
Science is not a means of creating facts. If that were the case, we would be stuck with many situations that would not be as good as the ones that we have. Our understanding of the universe is always changing when we get new information. I'm sure the earth is old, but I don't think our estimates are exact.
No, I would have to disagree with the notion that the age of the earth has been proven beyond question. We can generally date the age of the earth through rocks and some geological measures, but I don't think anyone can ever truly find the exact age of the earth.
Nothing in science is beyond question. That's the very nature of science, asking questions, even on topics we are already familiar with. Still, I haven't seen much reason to doubt current estimates. Science may very well come up with more accurate methods in the future, but I think we can be reasonably sure of current estimates.