I think in this case it's like driving a car, flying a plane, speaking Mandarin, or performing surgery- at which point is someone proficient enough to call themselves a developer?

Knowing only about 1% of the commands, code, and frameworks available to a top iOS developer can still produce some impressive results.

Teaching a child to write a fart app in 8 weeks- easy.

Teaching a child to write a top 10 app in 8 weeks- next to impossible.