[Boatanchors] Coaxial cable question

[Y S Lee]

Hello;
     I have been using RG-8 and similar coaxial cables for my ham antennas
from 7Mz to 430MHz. Some cables are over 20 years old and still seem to 
work well. I am thinking of replacing some worrying that they may exhibit high loss
due to their age. Does some has information on cable loss versus age?
If they do age then what is useful life time of cables?
de HL1FB/WW6N