The City of Melbourne runs line dancing classes at the Jean McKendry Nieghbourhood Centre in North Melbourne.
https://www.melbourne.vic.gov.au/event/line-dancing
You can book online here.
Contact the Centre on healthyageing@melbourne.vic.gov.au or phone 9328 1665.
Aligned Dance also offers classes at various venues around Melbourne. Their other classes are open to all ages, but because line dancing doesn’t involve jumping or running, they are usually suitable for seniors too. Contact instructor Matt Coleman on 0409 250 907.