Batteries, for example, are good for about three years. Vacuum pumps will generally last for about 500 hours, and fuel tank bladders or cells will generally last 10 to 15 years, provided they are maintained properly. There are always exceptions to average life spans shorter and longer. Beech, in the pilot's operating handbook for the newest Baron model, listed the life span of the vacuum pumps at 600 hours. All time-limited components ought to be listed where the pilot can easily find the information.
Engines have a defined life, and there are several variables that can affect their longevity.
Frequent use is beneficial, since there can be a tendency for the cylinders to rust. Moisture in the air corrodes the interior cylinder wall, which then abrades the piston rings, resulting in high oil consumption. This by itself will not lead to engine failure, but eventually the engine will lose power. Time between overhauls, or TBO, is recommended by the manufacturer but is not considered mandatory for Part 91 operations. The engine is the part of an aircraft most prone to failure because it is the most complex and under the most stress.