When assigning an Apple ID to my child the birthdate was not allowed. They are 13.
I was trying to sign my children up with an Apple ID on my MacBook. When it came to their birthdate (twins) it would not accept my entry. They are 13 as of 11/12 (birthdate 11/12/04). I had to make their birthdate 12/12/04.
kinda crazy....
(my computer's date is correct)
MacBook Air
OSHigh Sierra
10.13.1
MACBOOK AIR (13-INCH, 2017), macOS High Sierra (10.13.1)