I seem to recall that my first sensei often said "the more naturally talented the person is, the more it hurts when they hit the wall, which everyone eventually does." As far as minimum requirements go, USAF requirements for training days between tests, are higher than just about any other organization. I know that when I tell people here in Japan who adhere to Hombu standards, that I had to practice three hundred days between nikkyu and Ikkyu, their jaws drop as they say "Takusan desu ne, nande?". Here It is Seventy days from Ikkyu to Shodan.
Shodan in some places is a statement of "memebership" to the dojo. America has this connotation that a dan equals some level of mastery... which is silly. IMO