I found this thread from last year that might help:
It basically says this:
"Plat 5 star status is only for a very, very few people out there. It is basically someone who either lives at a high end Marriott property, a person on the Board of Directors of Marriott or some other influential person (like Mitt Romney). It appears the designation is given by Mr. Marriott personally."
"our team confirmed that the Platinum Five Star is not a status members can earn. It is a VIP status."