Age doesn't mean much if it was installed correctly and maintained. If the antenna still works, then you are good.
If you feel it's failing, then replacing the antenna AND the coaxial cable may be a good idea.
Discones can be a good option for scanner listeners that want to make the most of the frequency coverage of their scanner. If you have a specific system you want to listen to, then a band specific antenna will easily outperform a discone.