Generally speaking, cabling problems in domestic installations fall into two categories. Either that cable insulation is not of the correct type or cabling that does not have a circuit protective conductor (CPC) or earth.
All domestic installations built since the late 1960's should have flat PVC Cabling installed. Cable manufacturers vary in their exact opinion on how long these cables will last but it is generally accepted that provided these cables are installed correctly and not exposed to the elements or extremes of temperature they should last almost indefinitely.
Up until the early sixties and before plastics were widely available standard electrical cabling insulation was made from rubber, with coloured insulated inner cores protected by an outer insulation which was impregnated with a chemical to stop it drying out and breaking down. Unfortunately the inner cores weren't treated so where these inner cores are exposed (ie. behind light switches, sockets, ceiling roses and in junction boxes and consumer units), the insulation has a tendency to dry out and eventually just crumble away. The length of time taken to reach this stage varies greatly from installation to installation but is exacerbated by low humidity and/or excessive temperature (either from overloading or high ambient temperature). Where rubber cabling is found the lighting cabling will almost certainly have no CPC either which compounds the problem of the insulation breaking down.
In all cases, without exception rubber cabling (sometimes called TRS or VIR Cabling) must be removed and replaced with PVC/PVC cabling by an electrical contractor.