As with any car -- find out as much about the history of it as you can. If it's from the S.E., rust shouldn't be an issue, assuming it didn't come from the coast. Get it on a lift if you can --- nothing like getting under one. Corrosion and leak checks will tell the tale. See if there's any history on regular fluid changes -- all of the fluids. 20+ year old PS, brake and driveline fluids are not ideal. Not a deal breaker -- just something to tend to quickly and help you with price negotiation.

If it sat outside, ungaraged and undriven for long periods of time the interior plastic bits may be in rough shape. Check the date codes on the tires. Probably not worn out in 20k miles - if the original tires are on it (22 years old) -- I wouldn't go very far or fast on them.
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82 242-6.2L; '17 Mazda3; '16 Crosstrek