AO3, unlike a sex shop, was not created for exclusively adult content.
AO3, like a library, has content of all types, suitable for all ages, people in different stages of life, people from different backgrounds, people with different interests and needs. And like a library, it doesn't regulate who gets to see which parts.
For those who don't have the ability to figure out if it's suitable for them, it is not AO3's job to keep them away. Parents are responsible for managing their kids' access to media.
When I had young kids, I managed their internet access. I pointed them at sites I trusted to be safe and appropriate for them, and steered them away from sites I thought were dangerous for them. (...Like Facebook. And Twitter.)
My kids trusted me, so they went along with my recommendations. Especially since the safe sites included Yahoo's collection of Flash games, which meant they always had plenty of interesting things to do.
If my kids had not trusted me, I might've installed some kind of net-nanny program.
I did not, however, go pester the creators of Twitter and Facebook and say "you have a lot of toxic content on here that is unsafe for 10-year-olds and young teens; make it go away." I did not pester them to block all young teens from using the sites. Other parents have different standards from mine; it's up to them to figure out which sites are safe for their kids.
It is not AO3's job to figure out what's safe and reasonable for kids to read.
Can we get back to that "simple safety regulations" thing? Because that? That's pure bullshit.
There is NOTHING SIMPLE about age verification online.
What do you want AO3 (or any other site) to do - demand a copy of someone's photo ID?
All adults don't have photo IDs; I guess the ones who don't shouldn't be online.
Let's pretend they all have IDs, or all can get them.
Do you recognize every type of photo ID on the planet? Do you insist that the IP address connects with the address listed on the card? (So, nobody with VPNs, right?) (How many languages do your ID-checkers recognize?)
How do they prove the person setting up the account is the one with that ID card? What happens if a teen grabs their parent's ID?
...hey, then the parent can't make an account later because that ID is already used!
And assume you have that figured out.
What do you do with these IDs? Throw them out once the account is verified as an adult? (In that case: If someone says "hey this person is actually a child and you've been showing them porn," how do you prove in court that you had evidence they were an adult?)
If you keep the IDs... how secure is your storage server? How sure are you that you'll never get hacked? That a disgruntled employee won't copy the whole set and leak them online somewhere?
I repeat: there is NOTHING SIMPLE about age verification online.
Mega-corporations are trying to convince you otherwise, because they can throw a few million dollars at the problem.
...and still not solve it, because, again, there is no way to prove that the card or other ID being offered, actually belongs to the person filling out the account info.
(Do employers manage this? Yes... by talking to the applicant. By establishing that they know things that are indicated on the resume, and the name on the resume matches the ID card, and that, if the photo on the card looks nothing like them, or the address on the card doesn't match the one on the form they filled out, they have a reasonable-sounding explanation for that. You can do this with 15 people you are interviewing for a job. You can't do it with two million people signing up to use a social media website.)
All online age-verification systems are doxxing and identity theft waiting to happen.
In case people didn't know.
The OTW - the nonprofit org that manages AO3 and other projects - is deeply, vehemently opposed to tracking IDs. We remember when people lost their jobs and custody of their kids based on what kind of fiction they read or wrote, and we are not going to be a part of the current wave of witch hunts.
There is not going to be any kind of identity verification to use AO3. Ever.
The OTW does not judge you for your taste in fiction or what you like to write, and the OTW exists to stand between you and the forces of capitalism that want to control your interest in and access to art.
If the commenter above doesn't want their kids reading stuff at AO3, they can block their kids from it.
If the commenter doesn't want other people's kids reading AO3... that's none of their damn business, any more than it is Elon Musk's or Tim Cook's or Mark Zuckerberg's or Sundar Pichai's.
And if you find your decisions about business ethics matching up with any of those people... maybe consider why that is.