I believe that 8 is too young. When my brother and I were 12 and 14, we would sometimes play with the guns in the home when we were unsupervised. I think it was a matter of maturity not of mischievous intent. When my sons were 10, 12, and 14, They shot up 10,000 rounds of #4 spot nails in the cabinet shop while I was out on an installation. They were hiding in the shop and cabinets while shooting at each other. Therefore, trigger locks are mandatory and muzzle safeties on the nail guns are mandatory. Nothing wrong with the time spent with the grandson. Nothing wrong with the gun safety course. However, the ownership of a gun and opportunity to use it may be for an older child. IMHO I wish you well.
thanks for your good wishes and you are most certainly welcome to your opinion .... our son is the formal and legal owner .... it will not become the property of our grandson until sometime down the line when he proves to be ready for such a responsibility .... until then it will be locked in a vault and will only be taken out under direct adult supervision