how long the wires for electrical existence please advise
No, the metal in electrical wire lasts a very long time. The insulation may degrade though. But it's many decades.
If the house was built in the 1970s, it may have aluminum wiring. Its terminations will probably need attention. If the insulation is brittle, it all needs to be replaced. If the wiring has been exposed to water, via flooding, I absolutely would check the insulation some places in the walls, low near receptacles and such. If you are altering the load, increasing power demand, you will need to run larger conductors.
Electrical demand normally increases with time which makes heavier conductors desirable for present ant future needs. Re-wiring is best done during renovation, since it becomes (prohibitively?) expensive once walls, floors, and ceilings are finished. Depending on the scope of renovation, new wiring is likely to be required to meet current Code. This includes a maximum spacing of 6 feet between receptacles (to prevent the use of extension cords), GFCI or RCD protection, circuit dedication for major appliances, and other changes in NEC (National Electric Code) since the original electric service was installed. Most wiring installed before 1950 has reached the end of it's useful service life, even if it is still functional. This is because splices tend to deteriorate, insulation becomes brittle, the ground path develops resistance, and other factors. Upgrading is normally cost effective, but the extent of renovation (building permit required?) determines what upgrading is required.
