I have no kids, so what I say is prolly worth less than what I normally say . . .
seems to me that giving tasks - splitting wood or using a firearm - to a kid would depend on two things
Physical strength/coordination, but also thinking ability. I think an adult that has never split wood before needs a lot of supervision in the beginning. From time to time I still misjudge physcis and nearly get hurt.
Giving an automatic weapon to an 8-year-old was stupid. Go ahead, flame me.
Like the videos on UTube where a petite woman fires a weapon and the recoil makes her lose control of the gun. Initially, it looks funny, but that's only because no one caught a bullet. Rather stupid, if ya think about it.
If it were me, I'd be guiding the 8 year old with an axe very carefully until I thought he knew what he was doing. And I'd make sure to note when he shows signs of tireness, as that's when accidents happen.
Don't let him run the 660 until he can start it himself