You don't attempt CPR until you confirm that the person doesn't have a pulse. The angle up on the edge of the pool and the way the kid was doing compressions were not doing anything. Trust me, I've seen and done effective chest compressions and that shit is HARD. A 12yo tapping on someone's chest might be well-meaning, but it's not CPR

That's definitely long enough to sustain brain damage and usually the upper threshold for bringing someone back. There's no minimum time you must wait before attempting CPR though.

If their heart is not beating then you perform chest compressions. If they're not breathing then you perform breaths for them. You never perform one or the other if their body is performing it already.

There's some argument about the breathing part of CPR. If the event was acute and recent, like someone collapsing while standing next to you, then there's some modern guidance that breaths aren't necessary, since there's enough oxygen stored in their blood already and pulmonary compression could be enough to sustain them until first responders arrive. If the event was an unknown time period, or in this case 6 minutes prior, then they probably need breaths too.

I saw the "they don't teach that anymore!" claim Walter White made in Breaking Bad about the breaths and looked it up. There's a lot of confusion about that proposition and the addition has probably caused more harm than good, since now a lot of people think that it's never required, which is false.

It's important to remember that in cases where CPR is actually needed, the person is already dead, or in the process of dying. You cannot do more harm. You must use extreme force to actually compress the heart. You will break their ribs and probably their sternum, but since they will die without assistance, broken bones are a better outcome assuming they survive without severe brain damage.