Why can't people vote under the age of 18?
The Australian Constitution and the Commonwealth Electoral Act 1918 (a law passed by the Australian Parliament) describe how elections should be run. The Commonwealth Electoral Act 1973 amended - changed - the 1918 Act to lower the voting age from 21 to 18.
There has been recent debate about whether the voting age should be lowered further to 16, but the Australian Parliament would need to pass a bill - a proposed law - to allow this to happen.
People voting in a federal election

Australian Electoral Commission
Description
A row of 6 large, purple and white cardboard voting booths. There are 3 people standing at the booths with their backs to the camera. They are looking down and filling in their ballot papers. Each booth is screened off from the neighbouring booths so that voters cannot see each others ballot paper.
Permission should be sought from the Australian Electoral Commission (AEC) for third-party or commercial uses of this image. To contact the AEC email: media@aec.gov.au or phone: 13 23 26.