In brazilian jiu jitsu few published guidelines or standards determine when a practitioner is ready for promotion; the criterion is generally determined by individual instructors and/or academies.
There are actual 6 distinct belt systems used in BJJ and each one is different.
The IBJJF, which is leading BJJ federation, maintains an extensive graduation system that takes into account time-in-grade and membership standing, but makes no mention of specific performance or skill requirements. When instructors or academies comment on the criteria for promotion, the most widely accepted measures are the amount of technical and conceptual knowledge a practitioner can demonstrate, and performance in grappling (randori) within the academy and/or competition.
However there are some exceptions. Often a master will have an input on the belt he wears. One notable example was Helio Gracie who wore a blue belt and as does his son Royce:
And Rickson notably kept on wearing his coral belt even though he was promoted to red belt.
However master Flavio Behring just hit a new landmark – he turned 80 years old marking his jiu jitsu journey as 70 years old.