In November 2019 changes were made to the laws governing the use of International Drivers Licences in Victoria. 
People using International drivers licence must change to a local licence within 6 months of arrival in Australia. How to do this is determined on an individual basis, depending on the country of issue of the existing licence, the drivers age and number of years driving. Copy the below link to VicRoads into your browser  for more details. 
https://www.vicroads.vic.gov.au/licences/renew-replace-or-update/new-to-victoria/overseas-drivers