Winston reading age

Winston read aloud from start to finish this

http://www.amazon.com/Sullivan-Street-Hello-Reader-Level/dp/0590308769

the reading level is 2.5.

I looked in to this and this relates to the grade in an american school.

http://community.babycenter.com/post/a29518541/ar_book_levels_-_what_do_they_mean

so for this one book he can read at the level of a 7.5year old

http://en.wikipedia.org/wiki/Education_in_the_United_States