The major hurdle is knowing what sorts of problems can be solved with calculus or any other sort of math.
Here in the U.S.A. we tend to teach math in isolation, no thanks to the idiotic reading, 'riting, and 'rithmetic crowd. None of these subjects can be taught well in isolation. It's almost like we want children to hate math, or at least think they are no good at it.
A child ought to have had some exposure to calculus and what it's used for by the time they finish middle school. In most of the world calculus is first introduced with basic physics, just as Isaac Newton and Gottfried Wilhelm Leibniz first applied it.
One nice thing I can say about our new age of social media is that it encourages some level of literacy. Every child knows that reading and writing are useful skills. Too bad there's no similar incentives for numeracy beyond knowing how much money you've got.