FIRST has robotics programs for kids from age 4 all the way up to 18 with increasing levels of difficulty, complexity, and competition. So, if he enjoys it, this could be something he does all the way through high school.
Your plans to make him code seems a bit overambitious to me...
Another commenter mentioned FIRST LEGO League, which is a great idea. However, it does require that you have a nearby league, and the experience is probably going to depend a lot on the quality of that league (funding, coaches, etc.) So if you have the funds (but not the time), starting out with the kits just at home could be a great first step.