Generally young earth creationists don’t believe modern dating methods are accurate. Explanations for why they wouldn’t be accurate vary. But as an example, in

Generally young earth creationists don’t believe modern dating methods are accurate. Explanations for why they wouldn’t be accurate vary. But as an example, in my understanding carbon dating is based on a presumption that atmospheric ratios of stable and unstable carbon isotopes have remained constant over time. But how do we know that to be true? Generally the different kinds of dating methods are also calibrated against one another, so then you get a feedback loop of false conclusions verifying other false conclusions. And then of course you get various points of data that could contradict dating methods. One that was mentioned to me recently is that a plane was found buried under several hundred feet of ice. Presumably if it wasn’t obviously an object from the last century it would have been dated to be much older. So goes the argument. Anyway, I’m not an expert on dating things or young earth creationism but the Tl;dr is that they don’t believe the dating method used to claim it’s 12,000 years old is accurate.