Here is a link to recent college acceptances and matriculations.
Not sure about the fourth year of a language — probably more AP level but best to check with OHS admissions.
As for math, I think it’s likely that some kids take calculus as a senior and many go well beyond that and probably some finish at pre-calc. If you look at the link below you will see a graphic of the math courses by level (middle school, high school, university level). A lot of kids start at ohs for the advanced math, and the upper level classes probably have about 12-plus students and the graduating class is around 70 so I think a lot graduate with one or more years of university-level math—but there are also a lot of single -course and part time students who aren’t counted amongst the 70 so it’s hard to extrapolate. My son took three years of university level math at OHS . He wasn’t at all atypical.
One thing to note is that almost all the kids universally love the required core (ie, philosophy) courses, even the avowed STEM kids. These courses are only at grade level and are required for full time students and available for part time / single course students as space allows. There are also university-level courses in all the academic subjects.
As to why the kids choose OHS. It’s an international school and many (including US kids) choose it because they want the rigorous, advanced academics and a like-minded academically-advanced peer group. Others choose it because the flexible schedule allows them to travel for — and concentrate on — a significant extra curricular like athletics or the arts. These kids will also benefit from the rigorous academics but may choose not to take advanced courses due to their time commitments elsewhere.
Please note that the math schematic linked below has a similar schematic for each academic area of focus . If you click on a course and scroll down, you will then see the relevant schematic.