Tbh I would be amazed if anyone in the government knows that Lemmy exists.

It would be unwise to base any sort of response on this assumption. Section 13 of the legislation is pretty clear:

(1) For the purposes of this Act, age‑restricted social media platform means:

(a) an electronic service that satisfies the following conditions:

(i) the sole purpose, or a significant purpose, of the service is to enable online social interaction between 2 or more end‑users;
(ii) the service allows end‑users to link to, or interact with, some or all of the other end‑users;
(iii) the service allows end‑users to post material on the service;
(iv) such other conditions (if any) as are set out in the legislative rules; or

(b) an electronic service specified in the legislative rules;

I'll cover these "legislative rules" in a sec.

Most of the lists of affected sites you see flying all around the place are misleading, because they're being used by the media to get engagement rather than helping people to understand the actual law. In short: every site that meets section 13(1a) above is bound by the law. Which includes aussie.zone.

Services that eSafety considers will not be age-restricted social media platforms

These exception lists are important. For reasons, the government has included a provision in the legislation to exclude sites from section 13(1a). There are a whole bunch of provisions in the overall legislation that hang on the magic words "legislative rules". There are in fact 24 references to legislative rules in the legislation. If you read the thing all the way to section 240 (yes that's not a typo), you'll get to this bit:

240 Legislative rules

(1) The Minister may, by legislative instrument, make rules (legislative rules) prescribing matters:

(a) required or permitted by this Act to be prescribed by the legislative rules; or (b) necessary or convenient to be prescribed for carrying out or giving effect to this Act.

In other words, the communications minister can ad-hoc declare that any site/service that meets the criteria in section 13 is exempt from this law whenever she likes.

correct

aussie.zone has less users and content than the comment section on an average mildly popular youtube video

Thanks. The only one of those I currently use is YouTube, and all they have to do to verify my age there is to look at the age of my account. Hopefully that'll be enough. Otherwise, they can accept my anonymised digital driver's licence.