First gun I shot with was a .30-30 rifle and I was 12 years old and probably a 100lbs. Then i moved right to a 7mm when I shot my moose and I was 13 then and not much heavier than I was before. As long as it fits right and they are able to control it then anything would work. I know that I have troubles with shooting some guns because my arms aren't long enough so you have to watch for length but other than that there shouldn't be a specific gun to start out with.