That would depend on what type of environment they were used in. Daily driving, about 5 years max. Offroad, about 3 years due to water/dirt/mud being stuck to the wires.
Check your spec sheet that came with the wires for the resistance check but don't forget to do the "bend test" on each wire for cracks and checking for arcing (white residue on wires), especially near the cap and plugs. Bend the wire around your finger and check for cracks. If you see ANY, change the wire.