If you use SGDK2 the right way, it can be even easier than version 1, I think, but either one can be pretty easy to use if you start with a framework. Get him started on the map editor. That part is the most fun and interesting. Just set up a project with some sprites and tiles already defined and just let him put things where he wants in the map editor (maybe ask him what his favorite game is and consider using that game as a framework with the tiles and sprites all cleared out so he can design his own level), and then play the game to see how it worked out. Once he's got a handle on the map editor, help him create another similar map and define a function to jump from the first map to the new map. Then see what else he's interested in. If he wants to change the way some graphics look or add some new tiles, show him the graphics editor. If he wants to add messages or other specific behaviors, show him how to deal with functions. Walk him through implementing whatever he wants to do, making it clear that games are pretty complicated things, but SGDK can make certain kinds of games and features easier to deal with, so if he wants to do certain tasks that are supported in the kit, you can show him how. Maybe after he plays around a while, walk him through the tutorials, and then he might be ready to create a whole game on his own.
It's very cool that your brother is interested in making games too and you're willing to help (as am I, BTW). Hope it works out well!