If you pay that you are crazy! looking right now on Ebay. I count over a dozen for 300 or less, one is still in the box! The DJI superstore sells them BRAND NEW REFURB for 500.
They have most likely Drained past the point that a charger will detect them. Charging DJI batteries to 100% and storing them without checking them every few weeks or so, is the number 1 killer of these Batteries!
If you do look around and click you will get to this...which confirms 14 as minimum age to take test but I do not see anything about the parent being able to vouch for the minor
I know this is the internet and anyone can say anything.
I just called the FAA UAS helpline and the most friendly and helpful person answered.
He confirmed the above.
Center by calling 844-FLY-MY-UA (844-359-6982).
If anyone calls to confirm...