Although I like the idea, I hunted with a young man a few years ago who carried one of the Rossis. It was unbelievably heavy, and he was miserable by the end of the first day.

I see young hunters at the range frequently, many of them reaching for all it's worth to hang onto an adult-sized rifle. With weight also a consideration, I think what I'd recommend first is finding a youth-sized platform. Most manufacturers offer some version of "youth" rifle, and some (like the Howa) may also come with an adult-sized stock for later.

Good advice to check your local laws before hunting with a .223. I personally prefer the .243. Recoil isn't usually intimidating, and although I have a number of chamberings to choose from now, it's the .243 that goes to the field after deer and pronghorns at my house. Other mild cartridges you might consider, but which are going to recoil a bit more (thanks to launching heavier bullets) are the 7mm-08 and .308.

Good luck!