However , there is a plateau between the ages of 15 and 18 where the number of hours does not fluctuate by more than 10 hours .
During the primary season , the number of hours of practice per age increases gradually between the ages of five and 15 .
There is a plateau between the ages of 15 and 18 where the number of hours does not fluctuate by more than 10 hours .
During the primary season , the number of hours of practice per age increases gradually between the ages of five and 15 .