By the way, my son is 12, not 10. I know how old he is I promise
That's what they all say.... that's what they all say... hah
No worries my friend. I'm 15 and also want to take up a career in game development/ game programming. I just started learning how to code 3 weeks ago. I've accomplished a simple text game about escaping a spaceship. It was difficult but once you get it and see all your hard work payed off. It's marvelous.
I'm learning the C# programming language so I bought a "for Dummies" book.
The best advice I can give for you and your son is it depends on his learning style and how he wants to go about it.
Also programming does require some wicked math knowledge so, he should get good in math if he isn't already. Although most of it is theoretical and probability. A computer science major in college often has you taking "2" math courses usually Calculus.
As stated earlier the more knowledge pre- college the better really. Good luck to your son and may his programming dreams come true