I got you. I didn't realize he was that sensitive. You may want to try a different approach. First you have to convince him that science can be trusted, and you might not be educated enough yet to do that.

For example, to get him on the road to having an old earth, you first have to convince him that radiometric dating of rocks is valid. In order to do that, you need to convince him that radioactive decay is real. An example of this is nuclear energy, where we split uranium 235 atoms through a process called fission. Each uranium atom that splits produces 2-3 neutrons, those neutrons then cause, 2-3 more atoms to split, producing even more neutrons. This is called a controlled chain reaction. An uncontrolled one produces an explosion like the atomic bombs used during WWII. Anyway, the process of splitting these atoms creates daughter products - new atoms are also radioactive. These daughter products will decay by the natural process of radioactive decay, the same one that occurs in nature, where the atoms keep decaying until they reach a fairly stable or completely stable point, where their decay is either very low or negligible. Because of the long period of reaching that point, these wastes have to be stored away for thousands of years, because decay takes a long time.

If you can teach him this, then he will understand radioactive decay is real. Once he accepts that, you can show him an example of a natural reactor that occurred in nature https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor. They know this because they studied the daughter products that are created along the way, and they can see traces of them in the rocks, and that is how they are able to tell how long ago this occurred.

As I said, this may be beyond you, but I think it is within your reach. Reach about these things - nuclear energy, fission, fission byproducts, nuclear wastes, and the natural nuclear reactor. and that we depend upon for radiometric dating.