What changes when your child turns 13 and 18

Two birthdays change what your child can do and what you can see, and both changes happen automatically.

Steps

At 13, your child may create their own account. Below that age the sign-up form refuses, and a parent or guardian sets up and manages the account instead.
About 30 days before they turn 18, you are emailed to say the change is coming.
On their 18th birthday, your link to their record ends. Their sections disappear from Your family.
If they want you to keep seeing their training, they ask the coach to invite you again after their birthday.

At 18 the young person becomes responsible for their own account and their own information. That is the law, not a club rule, and it is not something a coach can override.
Nothing is deleted at 18. The club keeps the record; you simply stop having access to it.
Between 13 and 18 your child can have their own login and still be a child in every safeguarding sense: no private thread with a coach, and session reminders go to you rather than to them.
Every link that ends at 18 is recorded with the date.