The problem with youth guns is that barrels don't stretch. Stocks are easy to lengthen, but before long, that 21-inch barrel that was easy for a new shooter to handle will be way too short to swing anywhere but the turkey woods.
Most kids can shoot longer, heavier guns than you, or they, think they can. A 26-inch barrel isn’t a problem once they learn how to hold the gun correctly, and it’s much easier to hit with. Have a gunsmith cut the stock down if it’s necessary and reattach the end when the shooter grows. If it’s synthetic, buy a shorter one.