DJ and I hosted a family of four who had never been fly fishing.  Everyone picked up on the technique pretty quickly but the long nymphing rig was still a bit much for 7 year old Dino.  His mom did let him hold a fish and he got to eat a lot of gummy bears!  His 10 year old brother did really well.  Every kid is different but 9-10 is a good age to start kids fly fishing.  We had a nice sunny day and picked up some great wild rainbows.