Man, I'm only 19 now but when I think back to 12th grade of high school when I was age 17-18, it feels like so long ago.
Yeah that's how it feels to me too, even though I'm 25 so it's been pretty long. 
I remember how excited I was for it to be the last year of high school, since honestly I really didn't enjoy high school much.
I didn't enjoy high school either and wasn't paying much attention to classes, I just wanted it to be over honestly.
They call it so many different things based on where you're from, like Australians call it Year 12 and we call it senior year.
That's interesting, I wonder if schooling system in Australia is similar to the US.
Well the majority of students in Year 12 over in Australia work towards getting an ATAR or OP which lets them access university courses, so it sounds a little different.
Oh I've never heard of that, it sounds a little harder to get in the university over there than here.
It also seems to depend on what part of Australia you're from, since south Australians have to complete the SACE for the same thing.