I don’t think the kids are in 2nd and 3rd grade, they’re tall for 2nd and 3rd graders

2nd/1st years refer to the years in high school i think. They have high school as first through third years, each one being 3 years

In Korea they have middle school year 1 2 3 and then u move on to high school year 1 2 3 so these kids are about 16~17

Ohhh okay ty