It depends. He probably could handle a .300 WM out hunting, because you'd expect him to shoot only once or twice at an animal. I never remember feeling the kick when shooting at an Elk with mine. However, if it's a new rifle with a newly mounted scope, all the shots taken to get it sighted in can take their toll even on a grown man.

If the young man and you decide to let him hunt with this caliber rifle, you might take on some of the punishing initial shots to get the scope close to what you think it should be and let the 14 year old zero it in with the final shots. Or if he does it completely, do it over several shooting sessions, instead of one.

I think my .300 WM Tikka is a heck of a rifle, but it did knock me back a number of times before I got it right where I wanted it.

Good luck!