Approximately 6000 years old.  This is one of those subjects that have the potential to turn into a heated debate (hopefully it won’t get to
that), due to two groups that always stand in direct opposite of each other.  On the one side you get the Young-Earth proponents who believe in the biblical age of the earth of about 6000 years and then there are the Old-earth proponents who believe in the secular age of the earth of about 4.5 billion years.  I see that almost everyone that posted here (except for mrfe ) falls into the latter group, agreeing that the earth is a gazillion years old.  I on the other hand, as you already derived from my opening sentence, think otherwise. Check this out:

It’s amazing what you can find if you take the time to do a little bit of "research".  What I’m sharing below is not my own original work or opinion (although I fully agree with it and it makes a lot of sense to me after I have checked it out myself).  I got most of the info from answersingenesis.com.   So kudos to the site.  I could have just copied and pasted all the info here, but that would be against forum policy and I would be guilty of plagiarism and laziness. So I have taken the time to cut through a lot of the jargon and detail and summarize in my own words, as best as possible, what I have found.  So don’t just take my word for it.  Go check it out yourselves and yes, it’s a
Christian website.  

TheYoung-Earth worldview simply came from the Bible.  So this means if you stand with this view, you of course have to believe that the Bible is the divinely inspired, authoritative, trustworthy Word of God.  If you believe this, then you must be a Christian, which I am (I can
almost hear the facepalms already ).  
Of course the Bible does not say explicitly anywhere that the earth is 6000 years old.  If it did, then it would be out of date the following year and one would expect that an allmighty God who possess all knowledge in the universe, wouldn’t make that kind of mistake .  What
God did is give a starting point or “point of birth” for the creation of earth.  If you know when someone was born, you can easily calculate their age at any point in time, right?  So, according to Genesis 1 in the Bible, the earth was created on the first day of creation. So doing a rough calculation:
Adam was created on day 6.  If you take into account all the genealogies from Adam and Abraham using the Masoretic Hebrew text (where most of the English translations came from) of Genesis 5 and 11 and add up all the dates, we get about 2000 years.  Apparently most Christians and secular scholars agree that Abraham lived 2000 B.C., that is about 4000 years ago.  So, Adam to Abraham (2000 years) +
Abraham to now (4000 years) = 6000 years.
Two of the most popular works that calculated and arrived at this date, was by Dr. Floyd Nolan James (The Chronology of the Old Testament, A.D. 1993) and Archbishop James Ussher (The Annals of the World, A.D. 1658).  They were not the only ones and Jones
listed several chronologists who calculated the age of the earth based on the Bible who’s calculations ranged from 5501 to 3836 B.C. (remember to add the 2000 years A.D. – that is up to now).  
The amazing thing is that these calculations were not only done by people studying the Bible, but there are also EXTRA-biblical calculations, done meticulously by many historians for the Age of the Earth where more or less the same figure of 6000 years has been calculated.  Young’s Analytical Concordance to the Bible (Peadoby, MA:  Hendrickson,  1996) lists William Hales’s accumulation of
dates of creation from many cultures. Their dates of only thousands of years are good support for the biblical date of about 6000 years, but not for billions of years.

So what about radioisotope dating?  Well there are massive amounts of info available on this, there’s first of all a lengthy explanation on what it is and how it works.  Things like Uranium and Parent and Daughter half-lives are mentioned and a whole bunch of other stuff which you guys can check out for yourselves.  It’s just too much to mention here.  I’ll get straight to the facts.  
Radioisotope dating is not that reliable, because we can test it on rocks of a known age.  In 1997 a bunch of scientists called RATE (Radioisotopes and the Age of the Earth) investigated assumptions commonly made using radioisotope dating.  Their findings were quite significant and it had a direct impact on evolutionary dates of millions of years (REFERENCE - L. Vardiman, A.A. Snelling and E.F.
Chaffin (Eds.),Radioisotopes and the Age of the Earth: Results of a Young-Earth Creationist Research Initiative, Institute for Creation Research, Santee, California, and Creation Research Society, St. Joseph, Missouri, 2000.)
They took eleven samples (solidified lava) from an active volcano, Mount Ngauruhoe, which is located on the north island of New Zealand. They of course used radioisotope dating on the samples.  These rocks are known to have formed from eruptions in 1949, 1954 and 1975.
They sent the rock samples to a respected commercial laboratory – Geochron Labs in Cambridge, Massachusetts – and the ages of the rocks ranged from 0.27 to 3.5 million years old (REFERENCE - A.A. Snelling, The cause of anomalous potassium-argon “ages” for
recent andesite flows at Mt Ngauruhoe, New Zealand, and the implications for potassium-argon “dating,” in R.E. Walsh (Ed.),Proceedings of the Fourth International Conference on Creationism, Creation Science Fellowship, Pittsburgh, Pennsylvania, pp. 503–525, 1998.).
These rocks are known to be less than 70 years old and it is thus apparent that the first assumption made was false.  This is just one example.  So how can radioisotope dating be trusted on rocks of unknown age, when it fails to give accurate dates on rocks of known
age?  Think about it.

I though about it but... nah.

The earth is 4.5 billion years old or something to that direction.

alsonic:  It says right there, 7 days.  If God said 7 days it's 7 days.  Not 1 day = millions of years as many would like you to believe.

The earth is 4.5 million years old.

I really don't know I am not a scientists but all I know is it is over 1,000,000,000 years old that's all I know for now maybe I will figure out later on in life.

I'm not exactly sure how old the earth is, many people in life will and can debate on the truth but nobody on "actual" earth knows the truth.. maybe a estimate around it but not the exact number. If I had to guess though "billions" of years.

Uhh really old? xD
If I can remember years back to my school days in science class, the earth is like 4 something billion years old.
But how accurate that is I wouldn't know, the earths birthday isn't really something I make note of

Well do you want a Biblical view point, well you didn't post this in Christian Conservatives, so... In a scientific view point I think 500,000,000,000 years (I hope I made trillion correctly).