My son started shooting his Savage .223 when he was 4. It fit him well and he is very comfortable shooting it. The gun has killed 5 deer, although my son shot a small buck earlier this year and we tracked it for 4 hours with good blood trial then the blood dried up. So, I could see how some people are concerned about the size of a .223, but I think it was more of a shot placement problem. He shot a little to far to the back, by on 2-3", but that's all it takes.I'll try and link a video for you to see him shooting it.
ETA- Here is the link of the video, it's Fakebook so let me know if it doesn't work and I'll try and post it another way. Shooting the .223 at 4 years old
This post was edited on 1/9 at 9:51 am