[quote=Tarquin]
I'll put my name down for this. Just for reference, what kind of age range are we dealing with at this school?<- Is not American and is used to High Schools with with anything from 13 to 18 year olds
[/quote]

Ages 14-18. It'll be divided like a normal American High school with four years.

Freshman: first year (14-15)
Sophomore: second year (15-16)
Junior: third year (16-17)
Senior: fourth year (17-18)

But it's entirely possible for a character to be younger/older as a student. For example, a student might have skipped a grade, or did something abroad that pushed back their schooling by a year or two. (Like a peace corp-esque thing or something?)