It's to the benefit of evolutionists to go for the really old earth model. It's the only thing that will allow for enough time for their theory so that they can (try to) convince others that it's valid.
The ToE demands a very old earth. Take away the old earth and their theory has nothing to stand on.
But even if one were to "agree" that the Earth is 4.5 billion years old, that still would not be enough time to explain how "natural selection," working on "dumb" matter, produced the biological diversity that we see all around us today.
The evolution from bacterium to man, hypothesized as fully explicable as the outcome of matter + "random" process — i.e., as a trial-and-error sort of thing — seems to involve a huge stretch of credulity. For how much time would it actually take for a trial-and-error process to produce man — not just from a single-celled organism, but from matter itself?
And, by the way, how does such an hypothesis account for the rise of mind? There is a vast categorical difference between the "mind" of a bacterium, and the mind of homo sapiens sapiens. But if both are simply the result of material "accidents" constrained only by "natural selection," how much time do we actually need for man to occur, and what particular "hidden genius" must non-living, inert matter possess in order to account for this result?
Case in point, abiogenesis, which holds that life "spontaneously" arose from non-living matter. Yet the credulous person does not ask: Where did matter itself come from?
Plus there's no explanation of where "natural selection" came from. It's just suddenly "there." And looks to me more like an act of faith than anything else.
You don't need a "young" — i.e., six-thousand-year-old Earth — to raise these issues.