When purchasing, how old is too old and how many miles is too many miles?

Update here.

Found one totally overfilled with oil at a dealer and they told me “The guy who was working on it has been doing oil changes for 25 years”. He’d obviously been doing them wrong for 25 years.

Found another with a bent frame.

Found a first gens Tundra with a dangerously rotted frame. The sellers face when the first thing I did was look under the truck was priceless. He also told me the “Timing chain had been changed”. These are timing belt trucks with an interference engine that’s such a crucial detail. It blows my mind the lack of knowledge people have about vehicles and how sellers completely and ruthlessly capitalize off it.

It’s the Wild West out here at least for first gens. I’m sure newer vehicles are in much better shape