Wait till he grows up a little. If he finds the recoil of a .410 too much don't force the issue you could turn him off or scare him with a high powerd rifle. In a few years I would get him a Rem .260 or a 7mm-08 these have plenty of power for deer and are light on the recoil. If you reload you can back them down even further , and still have lots of power for deer. Some things ae worth waiting for.