Are we worried about metal ageing of the air tube on PCPs?
Dive bottles need to be tested periodically for corrosion and cracks, what if an air tube let go whilst the gun was in your shoulder?
Some time ago I decided to avoid the bottle-as-a-butt pcp air rifles (Gunpower, NP02 etc), rightly or wrongly that just looks like you're asking for it.
A pre war springer can still shoot like the day it was made and can be serviced for buttons.
Depends what you want to do with it I guess.