average

Itachi had spent his whole life training as a ninja; he didn’t have an ounce
of energy to pour into anything else. He just barely remembered the names
and faces of the students in his own class. He didn’t know anything about
students in other classes or grades. So he was assuming, based on their
height, that these students were in the most senior grade.
The average age of graduation from the academy was twelve. The
physique of seven-year-old Itachi was completely different. He was so short,
he had to look up at the students standing before him.

Itachi Shinden: Book of Bright Light Chapter 1 Part 3