I should have added an asterisk. Most times tires of that age that come in are showing dry rot, cracking, uneven wear, etc.; it's not a blanket statement. My dad's '15 Panamera Turbo had 40k on it when I bought it, but the tires were 2015 date coded and showing a bit of dry rot. Automatic safety fail - needed brand new rubber immediately.
Any of these things should fail a safety. I will not compromise the safety of any vehicle I drive, and will advise my customers of the same. Think that's a cash grab, have at it.
Also, if you want to challenge tire age, two words: Paul Walker.