Have you considered a glider? If he has good fine motor coordination, these can be a nice step up from Legos and rocket kits. My now engineering college student built his first remote controlled glider when he was ten and just kept building harder ones. Some are fairly straight forward kits- others require completely manual wiring for every part of the glider and the remote controller, so there is a kit that should match just about every skill level. Here is a good website that describes the different types:
http://www.cumulus-soaring.com/models.htm
