Is it possible that, influenced by some Chinese, Indonesian and Indian people, the Australian Aborigines develop a civilization (perceived by the western people as "civilization"), so that they reach an Aztec level by around 1400 AD?
The issue is lack of a crop that can be farmed in a way that it allows for agriculture. For an ATL where such a crop does exist (The red yam) see
https://www.alternatehistory.com/discussion/showthread.php?t=286304 (Land of Red and Gold Act II, which has links to the original)
It seems more likely that an early introduction of Asian agriculture to Australia would lead to a civilization built by Asian incomers and their descendants rather than an aboriginal adoption of agriculture - though there'd likely be a notable aboriginal genetic element to the civilization due to contact and intermarriage. The unassimilated aboriginal cultures would become increasingly marginalized, though some of them might survive the same way "Negrito" groups still exist in Southeast Asia.
Introduce cattle and then you've got the dung problem... with native states probably finding it harder than the British did to identify & import a relevant species of dung beetles as a solution.Wheat and cattle are the top agricultural products today and they were widely available in Asia for thousands of years.
Introduce cattle and then you've got the dung problem... with native states probably finding it harder than the British did to identify & import a relevant species of dung beetles as a solution.