The duty-free allowance for cigarettes when entering Australia is up to 25 cigarettes or 25 grams of cigars or tobacco products. This means you could bring in up to 25 cigarettes duty-free.
In addition, you can also get up to a total of AUD 900 for general goods and 2.25 liters (approximately 2.6 standard bottles) of alcoholic beverages.
The provision for cigars/tobacco products and alcohol, however, does not apply to ages under 18. If you are under 18, you can only enjoy a duty-free allowance on general goods.
Please note that customs regulations can change over time, so I recommend checking the latest information on the Australian Border Force website or contacting Australian customs authorities for the most up-to-date information before your travel.