Not to sway you away from the Ruger but Howa has a youth model of the mini action 6.5 Grendel with 12.5 length of pull. There is a package Whitaker guns was selling that included a black youth stock and a green full size stock. Whitaker list the youth model for $359. At one time the youth model could be purchased with a 22 light weight barrel or 20 heavy threaded barre. You could buy a Howa action in 6.5 Grendel and find a youth stock.
https://whittakercountry.com/product/79783
https://whittakercountry.com/product/79783