Well, the oldest tree is 5062 years old. But how do you KNOW that the oldest texts were 3000 years old. It's not like they had a date on them ?
Take carbon dating. We know how long the half life of Carbon 14 is. We know that the ratio of carbon 12 to carbon 14 is constant in living things, but carbon 14 decays and isn't replenished after they die. Therefore we can date organic things up to about 50,000 years.
Oh, before you dispute carbon dating, how do you think they dated early texts ?
How old are the dinosaurs ? Do your research. There is a whole wealth information that can be found on Google. It comes from many different independent sources, so we can be reasonable sure it's reliable.