The air systems are good for 15 years from their born date, but need to be tested every 5 years.
You need to buy a Low Pressure air system (450psi output) and make sure of the born date when you buy, as a few shops are selling systems that are a few years old, as new. They may have not been used, but as you can only use them for 15 years, if they were made 2 years ago then you only get 13 years life from it, and should be cheaper in my eyes.
Lips are a good safe company to buy from, but you will get some good deals from the classifieds on here.