I think Disney's "no under 14" rule is good, as believe it or not the park DOES have weirdos around, although you can't really enforce it 100%, as it is so easy to lie about age, since not every teen has an ID and they can look older or younger than their age. I'm almost 22 and look 17 at most haha. Also, with a parent note, that can be forged in a blink of an eye.
The other issue is, there's always people who act younger or older than their real age. That's why I honestly don't judge based on age alone. I've known or seen people who are in their late 20s who act worse than certain teens, and I know some teen(s) (you know who you are....
) who are more mature and intelligent than some 20 year olds. So...it's honestly hard to tell.
But definitely under 13 they should be with someone 18 or older.
As for HHN? That's what I have a bigger problem of, simply because of the situation that happened last year. But in that case, the blame should be on the parents and not Universal.
It's a tricky issue, but for me as long as the guest isn't going crazy around the park, I don't care.