A counter to that argument is Andre Galvao, who found that that he was NOT a natural grappler, both from his first instructor, Careca, and his own personal opinion. He also started at a "late" age, beginning seriously at BJJ at 17. He found that he picked up techniques slower than other students, but credits his success (which rank up there with the anyone, no one denies that he is one of the best grapplers in the world) with his work ethic. He came with the mindset knowing that he knew he had to outwork everyone to be successful.
So, judging just by skill level and accomplishments that "This guy is a natural because he accomplished all of these things, and he started at later age," is debatable. Jacare may or may not be a natural grappler, I'm not trying to argue with that, but the term natural in itself is very wishy washy when applied. Sure, it can be said that someone who works his ass off everyday for years upon years but has no success is NOT a natural, but when it comes to successful athletes, the term becomes hazier.
If a kid starts wrestling at 4, and by 18 he is considered the best wrestler in the nation, does that make him a natural?