He implicitly accuses (in nomine Ken Ham): “you don’t trust the Bible”. And then builds everything on the assumed validity of his accusation. From that point on the rest is noise, and no-one hears each other. Discussing the science merely gets drowned out in that increasing multi-decibel white noise.
Perhaps forget the science. Refute head-on and with confidence his initial accusation. He accuses you of “not trusting the Bible”. His accusation against you is an untruth. (You might, if you choose, go further and call it a lie and slander: but that’s a pastoral call in the moment!) Call out that untruth. Expose it. Refute it. Don’t go a step towards any science at all until he backs off his “you don’t trust the Bible” accusation against you.
I am increasingly convinced that science arguments against YEC pseudoscience are a waste of time… until the YEC at least can at least accept that you “trust the Bible” just as much as he says he does.
For our apologetics, the science is merely secondary and often a distraction. Primary is our defence of our respect for God-breathed scripture up to at least the level of the most “biblical” YEC.
(By the way, I have cast this as “he”, simply and solely because Randy’s visitor is described as “he”!)