So how old is the earth?
It’s old enough for what it was needed for.
How’s that for an answer :-)
Genesis is actually silent on that, saying nothing about the age of the universe or earth before Genesis 1:1.
And we need to be careful not to misunderestimate (bushism) the need. There were critters crawling the earth well before people ever walked it. All of this meant something to the Lord. The scriptures tell us so. A righteous man is kind to (regards the life of) his beast. You (the Lord) preserve man and beast. The lion roars and receives its food from God.
God got glory in all of these things too. The ultimate act in this play was mankind (us) but that doesn’t mean there were no preceding meaningful acts in it.
I try, more or less valiantly, to dodge exact age questions. The scripture isn’t tailored to our curiosity. Day-age is possible and there are some intriguing suggestions, but couldn’t be proven by any science we know. (Why don’t the creation accounts tell us of any noons or afternoons?)
Time is relative. From our perspective on Earth, it may be billions of years, yet from a perspective elsewhere in the universe, Earth's age will vary. Gerald Schroeder, an MIT PhD in nuclear physics, a former member of the United States Atomic Energy Commission, and a teacher at Aish HaTorah College of Jewish Studties in Jerusalem, believes that from the perspective of the point of origin of the 'Big Bang', the universe has just begun its sixth day. He suggests that if the universe is 15 billion years old from the perspective of Earth, from the perspective at the origin of the 'Big Bang', we have just finished the sixth day. His theory is based on Einstein's Theory of Relativity.
Evidence for the relativity of time was shown in the Hafele-Keating experiment. The link also briefly discusses the University of Maryland experiment conducted in late 1975 and early 1976 which Dr. Schroeder discusses in several videos posted on Youtube.
I can't say as I necessarily agree with the Doctor, but I believe there is too much evidence against a 'young Earth' of 6-10,000 years that Young Earth Creationists (YEC) claim. Likewise, since evolution, at least 'macro' evolution lacks evidence, Old Earth Creationism (OEC) is also suspect in my view.
Since nothing of Jesus' existence and teachings in the Gospels have ever been discredited, and nothing in the other books of the NT has been found to be incorrect, I'll stand on, and trust His Word, that He is God and His Word is true. Since He never 'corrected' any 'errors' in the OT, including Creation and the Fall, as outlined in the Book of Genesis, I'll take it at face value. 'Everything', including time, space and matter, were created by God, in six days. Does that mean six days on Earth? Not necessarily since in Genesis 1, the Earth is not created on the first day, so how can a 'day' be measured when the point of reference has not yet been created?
Whether Dr. Schroeder is correct, or OECs, or YECs are correct, or none are correct, it does not matter to me. As noted above, there is no evidence of falsehood or error in the NT, so I must believe Jesus is who He said He was. Since He made no 'corrections' to the OT, then I must believe that God created everything in six days, however He defined 'six days'! Jesus only corrected the actions and interpretations of the Pharisees and Saducees, who, having spent their lives studying and interpreting the Tanakh, BADLY misinterpreted God's Word, to their advantage, against the people.