A true "youth rifle" will have a shorter than normal length butt stock.
Most will have 20" barrels, but I think that's a mistake. I think the ideal beginners youth rifle or a newbie woman's hunting rifle, should have a fairly long barrel so that the pressure behind the bullet will have dissipated by the time the bullet exits --less noise, less muzzle flash, less concussion in the air.
A skinny sporter weight barrel with a 6 mm (.243) bore will probably only weigh 3 oz. more if it had 6" longer barrel.
I think that would be ideal.