Aircraft life
Lots of comments in this post are about OLD 10 to 15 year old jets.
10 to 15 years old IS NOT OLD. This sort of aircraft is designed for an economic life of at least 30 years 80000 hours and 80000 landings.
Lots of well financed or very credit worthy airlines rollover their fleet at between 10 and 20 years but this is purely a financial decision. It is not based of the aircraft being “worn out”.