USEF defines “age”:
GR103 Age (of Individual)
- The age of an individual on December 1 will be maintained throughout the entire competition year.
- Persons born on December 1 will assume the greater age on that date.
- If a competition is in progress on any November 30, an individual’s age at the start of the competition will be maintained throughout the competition.
- Exceptions: see GR150, EV104, DC912, DR119.3, EN102, RN104 and PF106.1-.4.
The definition is the same whether it is being able to compete as a junior, or sign as a trainer.
So, if she is competing as a Junior, she can NOT sign as a trainer.
Here is the USEF definition of Trainer
GR148 Trainer
- Any adult, or adults who has the responsibility for the care, training, custody, or performance of a horse.
- Said person must sign the entry blank of any Licensed Competition whether said person be an owner, rider, agent and/or coach as well as trainer.
- Where a minor exhibitor has no trainer, a parent or guardian must sign and assume responsibility of trainer.
- The name of the trainer must be designated as such on the entry blank. See also GR404.
The USEF doesn’t require the Trainer to be present at the show.
BUT the USEF will hold the Trainer responsible for any violations related to “care, training, custody, or performance of a horse” - especially any drug violations - whether the trainer is present or not. So the TRAINER may not be willing to sign the entry blank if they are not going to be there, and I would not blame them.
(I am not a steward, but I am a TD.)
The usual practice, when the regular trainer can not or will not sign as Trainer on the entry blank, is to have a parent sign as Trainer.