It's never too early for safety training and rules. My Dad and grandparents had rifles accessible in the house, and as far back as I can remember, basic rules were drilled into me on safety. The guns were unloaded of course, but my Dad told me there was no such thing as an unloaded gun, and no kid was allowed to touch a gun without permission from an adult. Ever.

I don't remember how old I was when my Dad first took me out to plink cans, but I was small enough that a 410 shotgun knocked me backwards. I took to the .22 rifle, and had fun target shooting with it. I was never allowed to shoot without my Dad.

I never took to hunting, and my Dad quit taking me after a couple of times, but he tried. Fishing was fun, though.

As for professional range-type firearm training, it never came up in my family. If it was my own kids, 8 would be too young. Ten might be okay.

As for shooting an Uzi, 8 is definitely too young.