For a first gun I would get him a youth model break action, like a rossy or NEF/H&R or even a small bolt action like one of the crickets. The break opens should work pretty well no matter what hand he shoots with, and the bolt will be a single shot as well so it really wouldn't matter either.

I would check his eye dominance first. One way is to hold your finger in front of your face while looking at something far away. With both eyes open your finger should be transparent and you should be able to see the target thru it. When you close or cover one eye it will either shift to the side, or block the target. What ever eye it blocks the target with is your dominant eye.

Another way to do it is to place your hands together (overlap them making a very small triangle or hole to look thru) . Hold them out infront of you and look at something far a way thru the hole, then slowly move your hands toward your face. The hole should go to the dominant eye automatically.

For now I would get a single shot or a bolt action and teach him to use open sights. I feel open sights are easier to learn on when starting out because you don't notice how much you move. With a scope you can see how much you shake and move a round. It makes it much harder to get on the target and get a shot off when you can't hold still very well. This leads to target panic and jerking the trigger, which you don't want to teach him right off the bat.

When he gets a little bigger and more comfortable with shooting get him a marlin Model 60 or a Ruger 10/22 with a low powered scope if you want. Either of those should last him for decades if he takes care of them. A marlin lever action would be nice too. I had a Henry that was pretty nice as well for about half the price the marlins are. The marlin is a nicer gun as far as fit and finish goes however. That is actually the gun I learned to shoot on. My dad still has it and it shoots great even now.

I am also left handed, but I am right eye dominant. I do pretty much everything right handed as far as sports go. I shoot firearms and archery right handed and throw right handed. I can actually do everything but archery with both, but prefer right handed shooting. If you can get him to shoot right handed it will be much easeir in the long run, not a must though.

Paul