Interestingly enough, personality traits are pretty much solidified by age 7[0]. That suggests that 7 years old is not an arbitrary number in this study. [0]:

Interestingly enough, personality traits are pretty much solidified by age 7[0]. That suggests that 7 years old is not an arbitrary number in this study. [0]: https://www.livescience.com/8432-personality-set-life-1st-grade-study-suggests.html https://www.livescience.com/8432-personality-set-life-1st-gr...