Nothing is exclusive in the least. Anybody who can afford a ticket may fly F. That's pretty much true for most carriers. You don't have to prove your royal lineage.
As to who books when, you should know that many F pax are people who may book while enroute to the airport for a flight. Something comes up, they grab their "go" suitcase, car picks them up and enroute someone books them.
It is the other ranks in the back who tend to book months out.