What is the life expectancy of aircraft paint?

It depends a lot on the working environment of the aircraft. If it is in a salty environment like along the coast or on an aircraft carrier it doesn't last all that long. On the other hand if it flies mainly over land and is stationed in Pheonix Arizona it will last much longer. Also some areas around the body of the aircraft need more frequent attention. Areas around exhaust pipes on piston engines corrode pretty rapidly. Also the area where human urine is dumped overboard in flight on some aircraft corrodes very quickly due to the salt content of the urine. Don't worry... the urine will evaporate long before it hits the ground.