Chassis life really depends on how the car is maintained. For instance, if you live in the salt belt, and the previous owner didn't wash the undercarridge of the car...you could have potential salt oxidation and rust. Likewise, chips in the paint left untreated can lead to rusting of panels, etc. So, like grade said, have a mechanic check it out.

My Integra's chassis has about 171K miles on it, no rust whatsoever because I've been quite meticulous about washing the underbody and filling paint chips.