Welcome to the forum
First, you don't pitch with a 1st basemans glove, notice how it gets slung around and really is a huge problem? You see this a bunch in the younger kids, with the arm behind him like that...how do you think he will handle a liner coming right back at him? He needs a correctly sized glove...yes it is important. Now there are gloves out there that are correct sized and easy to break in (I like Mizuno because they break in really easy and nice "11 1/2" or "11 3/4" are as big as you need).
Once he's correctly outfitted...that front arm is a problem, look into the concept of equal and opposite (Search on YouTube or here), you want that arm out front and then bring the chest to the glove.
When you get this to happen, get some more video and we'll see what he looks like.