Will resistance of wire increase with age due to some effects?
Difficult to say without seeing the switches and wiring, but I would suspect a bad connection or wiring fault somewhere. You do not say if it has always been like this or if the fault has developed recently. One of the wire terminals on the switches may be lose or corroded, or maybe at the lamp, motor or distribution board.

I would very much doubt that the wires themselves have changed in resistance unless they are damaged and badly corroded. 

The solution is to ask competent electrician to examine the setup and remake the connections as necessary. You say you are "school boy electrical enthusiast" so PLEASE DO NOT TRY TO DO THIS YOURSELF if you want to eventually become an adult electrical enthusiast.