12th grade is the final year of secondary school.
12th Grade is the final year of secondary school, but did you continue and attend college? 
yes i did. you? Most countries student graduate at age 17-18.
I attended a technical college and studied Cosmetology. Here in the US we graduate at 17-19 depending on birth date. 
I guess that some countries has 13 grades.
If you consider Pre-k and Kindergarten as grades, we would have 14 grades here. What country do you live in? 
United States. In Australia, 12th grade is referred to as year 12.
I see a lot of other countries also refer to "grades" as "years". I think that is interesting to see how other countries refer to things. 
me too.  In New South Wales, Students can enter year 12 at 16 and not finish until they are 18?