I got my first knife when I was 8 or 9 and after sharpening it just like my uncle did I had it close on my nuckle nearly going to the bone. Needless to say I reccomend getting a LOCKING or fixed blade knife for a first knife. My brother gave his boys locking knives at the age of 8 as well and they have lost them a few times but have been rather responsible with using them.
They have asked me to make them a knife for quite some time but I thought that 10 was a good age for them to look after a super sharp custom knife in an appropriate manner. I made one for my eldest nephiew for his last birthday and I have one I am making for my next nephiews 10th birthday.
This is the knife that I made for him.