Some homes built between 1965 and 1975 were wired with aluminum rather than copper. While there have been some problems associated with aluminum, there’s no need for worry. Problems arise from the connections, and not the wire itself. Basically, any switches and plugs used with this wire must be compatible and approved for use with aluminum.
If you’re having work done, like an addition or remodeling, and you suspect you might have aluminum wiring, have it checked by a qualified electrician — someone who understands this type of wiring.