Return trip mandatory when leaving Australia? [closed]

Is it mandatory to plan the return trip in advance when leaving Australia (NSW) for 3 months? I ask because airport staff makes it look like there's a law or something without explaining further details.

If so, why, and how can you be exempt from this regulation?

Edit: Trip is to Germany.

Edit: As comments and replies suggest this is the wrong question. I explained the details in the comments myself. The whole situation has been miscommunicated to me.

Best Answer

3 months (90 days, to be exact) is the period for which a citizen of a visa-exempt country such as Australia is allowed to stay in the EU (the Schenge area, to be exact) without a visa.

If you want to stay longer, you need a long-stay visa (and a residence permit if it's longer than a year).