Javemn
Well Old man Rimmer inducted me to the noble art in a J-3 Cub when I was about 9 (ie tall enough to reach the rudder pedals) Even before that I was allowed to be in charge of stick and thottle. Unfortunately I fell in love with it from that moment on (the other woman is what Mrs Rimmer calls flying). Not only is it great fun for kids but its a handy learning tool – later on when I had mastered the art of flying a real aircraft (OMR was firmly of the belief - and still is, that no aircraft without a tailwheel is "real". Today he's added radial engines to that discription BTW) Old man Rimmer let me lose with his 310 but in return insited that I did all the planning for cross country flying - which of course taught me good practical maths as well as geography (Met and looking at topographical features from the air). He insisted that I study the physics of flying as well as the whys and wherefores of how the engine and aircraft systems worked and what happens when they don't - all sounds grim but I hoovered the infomation up and loved every minute of it.
I reckon if a kid is interested then its never too early to start. To qualify the remarks all this was A) a long time ago B) in the States. Legally speaking, its my understanding that under JAR-FCL there is no minimum age for dual flight but you have to be 16 for solo. But since time in the air is seldom wasted think of the advantage Javemn Jr. will have when old enough to take up training for a PPL and beyond.