I really don't understand the way math is structured in the US.

I studied geometry (and algebra) as part of the standard math curriculum starting in 6th grade in my home country. And in the math/science strand we certainly covered calculus in 12th grade (possibly starting in 11th grade) -- we needed those concepts for physics! But there was still geometry involved in 12th grade (and trigonometry).

And where does the idea that proofs are limited to geometry come from?!?

Math and multiple choice questions. How... sad.