In the United States, the average age of a student in the fourth grade is between 9 and 10 years old. According to the website CraftyMotherFather.com, the minimum age to enter fourth grade is 9 years old, and children might be older or younger if they have been promoted forward, held back, or had a birthday during the fourth grade that makes them a slightly different age than the rest of their class. In almost all states in the US, students must be at least 9 years old to enter the fourth grade, and there is some variation from state to state based on when a student’s birthday falls. Its important to note that age ranges can vary slightly depending on the country or educational system.