To the OP, your son, Alex, reminds me an awful lot of myself! I'm 16 right now, but when I was only 9, I really wanted to become a game designer too. 7 years ago, it was a bit harder to look for help concerning how to become a game designer, but over time, I learned a lot of valuable lessons and matured in a way that made my motivation to succeed as a game designer even stronger.
One really big advice to your son is to "Start early, start small". Meaning, if your child ever gets a hold of a really good game editor, tell him to start off with really simple projects and publish them over time. I recommend Game Maker 8 as a really good start. (http://sandbox.yoyogames.com/)
My mistake when I was making my games back then, was that I expected to make games that look professional like the ones I always played on my consoles, but I was getting ahead of myself. I just kept getting frustrated, abandoning project after project. It was only 2 years ago, when my father gave me advice that changed my life forever. "Start early, start small". I started with more simpler projects and published them over time, and it really helped overall with the recognition I was awarded with the people who played my games.
Your son has all the time in the world to make his dreams come true. Make sure he uses his time wisely on simple projects that he can publish online instead of trying to imitate the World of Warcraft MMO all by himself. Trust me, his games will improve a lot more using this "start small" method.
If you're looking for credible proof regarding my past works and accomplishments, take a look at this website (http://pdc-gaming.webs.com/). I just learned how to design websites a couple months ago and although I have yet to update the 'Mini-Games' portion of my website, within a week, it will show a good handful of games that I finished working on that you and your child can play for free.
Please, by all means, use my website as a reminder to your young boy that dreams do come true. He should never give up on his dream of becoming a game designer, for he already took the necessary steps it takes to starting up the rest of his grand journey for future happiness. Good luck to him, and thank you, OP, and everyone else for helping pave the path for this young, little boy's success. It warms my heart because that young boy is like looking at myself 7 years in the past.