So I will explain the swedish school system just so you don't get confused

6 years- 6-7 years old

first grade- 7-8 years old

second grade- 8-9 years old

third grade- 9-10 years old

fourth grade- 10-11 years old

fifth grade- 11-12 years old

sixth grade- 12-13 years old

seventh grade - 13-14 years old

eighth grade - 14-15 years old

ninth grade - 15-16 years old