Apparently all US states require 6 year olds to enroll in first grade. (homeschooling might be an exception) IIRC some of the nordic countries start school at a

Apparently all US states require 6 year olds to enroll in first grade. (homeschooling might be an exception) IIRC some of the nordic countries start school at age 7, but they require you to already know how to read and write before enrolling.