I am a college student who enjoys playing and creating games. I started at about the age your nephew is. The three things that helped me learn to program games were my TI-82 graphing calculator, the manual for said calculator, and my 4th period sophomore chemistry class, which is to say that I had a programmable device, the programming language reference, and time to devote to programming. Those are really the only things needed to program anything, including games.
I don't know of any courses that teach games (though you may search for a computer camp of sorts), but all that is really needed is a book.
If you go to a bookstore, especially a technology-focused bookstore, you will find lots of books on game development. Some books are basically cookbooks for video games -- you read it from front to back, follow all the directions, and at the end you have a video game that you programmed, but is just like everyone else's who bought that book. In many of these books, you are merely copying code from the book to your computer, and not actually learning to program.
There are also other books that focus on teaching the skills needed to program whatever game you desire. You can start reading at the front, but it will probably wind up being used like a reference book. These books may require previous knowledge of programming, or may only introduce parts of the programming language needed for game development. Usually, these do have one or a few small games that are made as the book is read, but the focus is on learning skills and knowledge, not just having a cool game at the end.
I would not recommend the former unless your nephew only has a passing interest in the subject. I would recommend the later if your nephew has a desire to learn to program computers.
You could also go the route of learning a programming language from a general purpose standpoint, and then applying that knowledge to create a game. I would recommend this course of action if your nephew has a strong desire to learn to program, and doesn't mind putting forth the extra effort to learn a programming language. I find that the "Sam's Teach Yourself [Whatever] in [X amount of time]" series works very well in teaching the basics of a programming language. Also, computer science courses would work as well, but they are usually upper high school courses.
Always read the introduction to a book, and possibly the first chapter, before you buy it. The intro will (usually) let you know who the book is and is not for, and what other previous knowledge (if any) is required.
Once he can program something to take input, work on the input, and output the result, then he can just let his imagination go and create whatever he wants.
I have a 13 years old nephew and he spends hours playing games (sp2 or 3).He wants to learn how to create games.
Where would he find resources to get started. Is there a course for kids.