| "5 guys from 19 to 21 from a fraternity"
"5 guys from 19 to 21 from a fraternity" isn't a protected class under US law.
"5 guys from 19 to 21 from a fraternity" isn't a protected class under US law.
AirBNB and their lawyers believe that US Law does in fact apply. They note explicitly though that there are certain classes of exceptions.
https://www.airbnb.com/help/article/898/ada-and-fha-complian...
That depends on local law; in California, it doesn't if you have exactly 1 roomer in a single-family, owner-occupied home. (There are still restrictions on advertising preferences, except gender, and then only when there are shared living spaces.)