[yzydserd]

Where I live, where many people live, we enter high school aged 11. We haven’t been introduced at school to geometry yet.

I suspect you’re using American terminology. When talking about school years it’s often useful to talk about the year or grade of school, like “9th grade” or “year 9” as it’s more universal.

[adw]

I’m not and, unfortunately, those aren’t universal either, even within a country. The normal terminology where I grew up would be S1, which follows P7.

I would expect most people to know about trigonometric functions by age 12, yes. (I entered high school at 11 and the first topic tackled in maths classes was elementary trigonometry.)