Usually only winter/spring to spawn in brackish waters. My biggest that was nudging 50cm came from over 30km as the crow flies from the first natural salt barrier. A mate got one over 55cm almost 20km upstream of the first natural salt barrier, and another mate got one nudging 45cm in a similar area that was as black as the ace of spades suggesting it's been way up in the fresh for a very long time. Fisheries study on the Snowy River Bass before stockings started had fish well over 40cm ping the acoustic monitors almost at the NSW border.
They grow dependant upon the size of the river and prevalence of food sources. Quite a few east coast creeks and smaller rivers do produce fish that struggle to hit 50cm based off peoples catches