Cabelas has the CVA Wolf on sale right now for $149

http://www.cabelas.com/product/Barga...3Bcat105651180

I have one and it would make a nice youth rifle. The stock is not specifically youth-sized, but you can check the dimensions and see if it would work for him.

Not a lot of options in .45 out there anymore. I have a .45 CVA Hunterbolt that has treated me well - if you can find a used one, you can cut down the synthetic stock yourself and add a new recoil pad on the end. I've played around with some low-power loads- 70 grains of powder and a 200 .40 cal XTP - recoil is very mild, like shooting a .410 shotgun with field loads.

If you get a .50 and are worried about recoil, use a .40/.50 sabot with a 200 grain bullet and a reduced powder charge. Hope this helps!