The fae does not prove a threat for the most part, unless someone of such an age is out of bed past midnight. At midnight, it orders them to go to bed, and only they are capable of hearing it's voice - the rest of us may hear creaking wood, or quiet rustling. Shortly after this time, it issues a warning. If one does not heed the instruction and the warning, it will repeat it again. Those able to hear it will then feel a swiftly increasing sense of dread they cannot shake.
If both the warnings and the fear are ignored, then the fae will come and find those it deems to be breaking the rules. It will do this regardless of where someone is. Those exempt from the age group will not see it - though they may see strangely moving shadows instead.
The extent of what the fae will do is yet to be seen, but in the few previous instances that it has been encountered, it has reportedly attempted to drag people back with it.
However, the threat is not absolute. After all, the teenagers serving in the Watch have seldom been trouble when taking a shift at night.
It seems to be a matter of permission. With the help of Yosuke, I was able to put this to the test. It seems that if a victim is given permission to stay up later than midnight, they will be left alone and untroubled.
Unfortunately, it seems that this must be repeated nightly. One grant of permission will not keep someone safe for the duration of their stay here.
I suggest that those who will require to be without such a curfew contact someone above the age of twenty-one in advice. Notably, it did not seem to matter when the permission was received.
It is my hope that this information may be used to bring an end to the dangerous situations that have arisen involving that particular fae. As always, if anyone has any questions, I will do my best to answer them.