A great age to start a young'un to fish. Hardest part is the casting. Train them at home with a yard. You try to teach them at the pond or lake and you might be doing some diving for that new rod/reel when they try to cast and release the push button at same time while still holding onto the pole.
You could also start them out on a simple bamboo pole and line setup, which is where I first started. I suggest this method. OR, get a good pole from Walmart and just get some 10# Spyder-wire or Monophyliment(sp) line and tie onto the rod tip with about 20-25 feet of line to act as same as a bamboo pole, then teach them on how to gently use the pole to swing the bait out into the water without losing the worm on hook. That's why you want to practice in the back yard. Use some lead sinkers on the end of line to act as a hook for safety to get them into the act.
I'd only go with a simple bobber, hook and worm rig. You'd be greatly surprised how they'll light up with catching some Perch/Bluegill/Bullheads and smaller Channel Cats with such a simple rig. It teaches them how to hook and keeping tension on the line and is the easiest to learn while watching for the bobber to go under. As they get to know how to fish, they can then progress to more advanced techniques of reels/rods and going for larger fish without using a bobber and how to tell when a fish is on the line by just a feel of the finger or rod tipping.
I'd start out at a pond that is stocked well or check with your local Conservation Dept to have them suggest some spots to fish with a new fisherman. Some conservation offices even have stocked ponds within eyesight of their main office as they usually every year have free fishing days for the youngsters. Trust me, I've even had lots of fun taking my Nephew to some of these.
Start with the simplest rig and work your way up as experience is gained.
