Perhaps one thing to say which may be useful, is that ‘calculus’ can mean a lot of different things, and the meaning can vary between courses as well as between schools and countries. When I was in high school, we did calculus in the last two years, and it was similar to the earlier years: you learned a bunch of algorithms for manipulating symbols, some of which required a bit of intuition for some step (make some substitution, for example), and you learned a few facts (about slopes and areas) to be able to solve word problems. The first thing we learned was a part of the differentiation algorithm: the derivative of x^n (where n is constant) is n x^(n-1). At university, we called the course analysis, though I believe other places may have called the same thing calculus, and it was about defining various concepts and proving properties about them. We may have derived the above rule in class (I don’t remember) but I think anyone would have been able to derive it from the definitions and proven properties. Such courses typically follow a tripartite structure: firstly sequences, series, and their convergence to limits; secondly continuity of functions and limits of functions; thirdly differentiation and integration (and maybe some version of Taylor’s theorem). This course structure hasn’t changed that much since Cauchy introduced a lot of the ‘modern’ definitions in a textbook (obvious exceptions are integration – known as ‘Riemann integration’).

I don’t know what sort of course this one is. It starts with limits so maybe more the latter kind, but I don’t really see how Julia would be very useful there. My best guess about the suitability of the course is that it may assume mathematical maturity that you may not have, rather than anything about programming. Mathematical maturity tends to mean being able to cope with precise definitions and abstract concepts without deducing a load of wrong things, as well as being able to follow the kind of argument that is a mathematical proof.