Didn’t he just say you find the age of the dinosaur by the rock, and the age of the rock by the fossils that we already know the age of?
But he didn't say, in that one line you quoted, anything about the several independent ways that we know the ages of those fossils - several different radioisotopes with different modes of decay, just for starters.
"The wretched world lies now under the tyranny of foolishness; things are believed by Christians of such absurdity as no one ever could aforetime induce the heathen to believe." - Agobard of Lyons,
ca. 830 AD