I’ve done hundreds of them, not necessarily to youth length but cut down and a new pad fit. Run a wrap of painters tape around the butt and mark the cut. Take the pad off so you don’t saw the screws. Set the angle against the fence on a table saw and cut it off. Clean the burr off the edge of the stock with an ExactO knife. Sand the cut lightly with a sanding block, making sure to keep it square, you’re really just scuffing it for glue anyway.
Sand the base of your pad flat. Put a liberal amount of Loctite 416 on the shell of the stock and put the pad on where you want it. Put a screwdriver through the rear action screw hole and use it as an anchor to stretch a length of surgical tubing around several times to hold the pad in place as the glue dries.
Once dry grind on a high speed disc sander until you scuff the painters tape, taking care to maintain the stock angles. Finish with scotchbrite pad and a little oil.
