Which means we need to somehow adhere to whatever the government deems necessary to confirm our userbase’s ages

As I see it, you have three options.

• Adhere to the regulations, whatever the fuck they end up being (frustrating that we're halfway through the year and there's still no clear indication of what that is). Technologically, who knows, this may be more difficult than it's worth. It may expose the admins to liability in terms of privacy laws. May also involve a financial cost if 3rd-party providers are required.
• Reach out to MPs and Ministers to try and seek an exemption. If granted, probably the ideal case. If not granted, it puts you on their radar pretty explicitly.
• Try to fly under the radar. If they had any sense, the bill would have required the Minister to name social media platforms to which it applies, or at least have included an automatic exemption for platforms under a certain size (say, under 1000 MAU, what have we got? Not that, surely). In the absence of that, it's likely (though not certain) that realistically nobody in Government knows about this place and no police are going to bother investigating it. Opens up major risk if those assumptions end up being wrong.

I can’t see any instance outside the country caring about this law. Why should they?

It's the same as the EU when it creates legislation and says "if you have any European customers, even if they're not in Europe, you have to comply". It's bullshit, and they know it. They can't even enforce it on non-European companies that do provide a service to people in Europe. This will be enforced by the big guys with a global presence, and it'll kill off small social media in Australia, while small social media elsewhere will just choose to ignore it.