I guess you mean for the invites? Idk, no reason anyone can't do them any time they want, I'm certainly nobody special(well, I am the one and only gigabits but...yeah) and their isn't exactly a reward other than loot(crossing fingers for a vanity or pink somewhere in the run).
EDIT: holy guacomole! 100 posts, hello senior membership XD can't wait to use the senior bathroom, eat in the senior lunch commons, and generally flaunt my awesomeness!!!
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