It does no good to debate these people; any evidence against their position is considered inadmissible.
You can point out that chapters 1 and 2 of Genesis tell different and incompatible creation stories: they'll claim that you must read them with the guidance of the holy spirit to truly understand them. Been there, done that.
Genesis says we're all descended from Adam in about 4kBC, and we're also all descended from Noah in about 3kBC (since the rest of mankind was destroyed in the world-wide Genesis flood.) You can bring in the roughly 10k years of Egyptian genealogies which make no mention of Adam, or Noah: they'll claim (without the slightest sense of irony) that the Egyptian genealogies are merely ancient writings of suspect provenance and uncertain accuracy. Been there, done that too.
You can bring in the entire science of geology, which gives zero evidence for and an entire scientific discipline worth of evidence against a world-wide Genesis-type flood: they'll bring in some mouth-breathing "geologist" who got a degree from one of the all-too-numerous fundamentalist "universities" to argue that the question isn't really settled yet, there's still scientific debate. Been there, done that, got the t-shirt.
You can point out that Genesis 1 is a poem. Instead of rhyme in sound, it rhymes in idea --- just like most other ancient poetry --- with day 1 corresponding to day 4, day 2 corresponding to day 5, 3 to 6, and then day 7 as a finale. You can point out that nobody takes Shakespeare's sonnets literally: "Ah," they say, "But this poem comes from God!" Yes, BTDT too.
Arguments from biology abound, of course: 5k years is insufficient time for one man's genes to diverge into the breadth of human genetic diversity seen today; you can't fit two of every species of insect in an ark, let alone the rest of the fauna; analysis of mitochrondrial DNA puts "Eve" at orders of magnitude before 4kBC; and then there's the whole fossil record of course. All the evidence in the world makes no difference: evidence does not change non-evidential belief.
And you're supposed to convince a JUDGE? That's the trap. Judges are pretty good at determining legal questions; they're about as good as a coin-flip when it comes to scientific questions. We bring in scientific evidence, this nincompoop argues legal blather, which will the judge best understand? If he was serious about the bet being fact-based, he'd offer to have the bet be settled by someone trained in determining the truth or falsity of factual claims. There are such people: they're called "scientists".
When I say "been there, done that", I mean just that. I was raised in a fundamentalist sect, and had most of my education in church schools. I spent 25 years being indoctrinated (it didn't stick, apparently) then 15 years trying to bring the church into the 20th century, and the last 5 years taking what is apparently the only productive approach. Here's the approach, for those who haven't figured it out yet: JUST LEAVE THE POOR IDIOTS ALONE.