The U-19 designation on Nexus athletes' membership is strictly a USA Field Hockey Membership category (as is youth, adult, coach and umpire). This does not affect an athlete's age-group classification in Nexus. Athletes are automatically assigned to the correct age group for the Nexus program, but for USA Field Hockey Membership purposes, all are classified as U-19 Members.
An athlete's age on December 31 of that given year determines what age group the athlete will be in for the following year. For example, if the athlete is 15 years old on December 31 and turns 16 on January 1 he/she remain in the U-16 division. Again, the age of the athlete on December 31 determines their age grouping for the following year.