…and you think 14-17 year olds won’t circumvent this in mere seconds? Like, they’d just sign up at an instance that doesn’t implement these labels, or doesn’t care about them, or use their parents accounts, or ask them, or an older friend to sign them up, and so on. Even if age verification would be widespread and legally mandated, I highly doubt any sufficiently determined 14-17 year old would have any trouble getting past it.
There’s a very easy solution that lets you rest easy that your instance is how you want it to be: don’t do open registration. Vet the people you invite, and job done. If you want to be even safer, don’t post publicly - followers only. If you require follower approval, you can do some basic checks to see that whoever sends a follow request is someone you’re okay interacting with. This works on the microblogging side of the Fediverse quite well, today.
What I’m trying to say is that with registrations requiring admin approval gets you 99% of the way there, without needing anything more complex than that.