How old must my wiring be ?

[Useless]

It's most likely knob & tube wiring in a home of that age. Unless a new code was drafted demanding its replacement, that old wiring would have been left in place. If it is knob & tube, your outlets shoud have only two holes for the hot and neutral blades of a plug and not the roundish third hole for the earth ground. Knob and tube wiring doesn't have an earth ground. If you do have modern receptacles, chance are that someone updated them so you could plug in heavy modern vacuums and lead cords that require an earth ground. Of course, that doesn't mean an earth ground is present. It just means that the they connected the hot wire to the black side, the neutral to the white side (the taller of the two blades) and left the little green screw empty. What does this mean for you? It means that the surge protector you have your computer plugged in to probably isn't going to do dick to protect anything.

Now that you are worried, here's the plus side; homes with knob and tube wiring often have lower electricity bills and fewer fires are caused by knob & tube than modern Romex wiring.

I used to drive a delivery van for a commercial electrical contractor. I am not an electrician.