yeah, also whatever age my sister is, thats what my grade is, if you have a younger sibling and need a system like this, they have to be mostly 6 years younger than you (she's exactly 5 years and 10 months behind, but for 10/12 months of the year, shes 6 years younger than me) so i can tell my grade using her age, i think its cause (at least for me), i waited 3 years before going to preschool, then my parents put me there, and after kindergarten (age 6), i was first grade, then my little sister was born, so yeah