My age was less of an issue at the grade school level, where students of multiple grade levels were in the same classroom (because it was a small school). However, things were not so easy socially once I moved to a public middle school, where everyone else in the classroom was of around the same age. The article refers to both social and academic benefits to being younger - my experience was the opposite for the former. Things were a lot easier when my classmates didn't know I was younger than them.