When you read or google the rules for importing used cars into Australia, you will only find the following information:
Australia country allows the importation of right hand drive vehicles that are 15 years or above on the date the landing.
No age restriction on used vehicles imported to Australia. Thus, Australians can import used vehicle of any age.
However they don't provide you the information on the three main points to take care about, before importing cars to Australia:
The model you are going to import shall not be produced in Australia and there are certain car models allowed by the government of Astralia to be imported. Allowed car models you can check from the following web site: https://rover.infrastructure.gov.au/Produce/wizard/e6b9206d-0a30-4783-afca-a7208f2f730f
Before shipping to Australia car has to pass the biosecurity (quarantine) inspection. In Japan it is done by JEVIC (Japan Export Vehicle Inspection Center). https://www.jevic.com/services/vehicle-maritime-inspections/biosecurity-inspection-australia.html
Any individual customer must obtain a Vehicle Import Approval (VIA) in order to import any vehicle from abroad. Please follow the link below for the ways to receive an VIA. https://www.infrastructure.gov.au/infrastructure-transport-vehicles/vehicles/importing-road-vehicle-australia