I'm ill prepared to answer, having never yet started a "young'n" flyfishing, but I have always believed that you start 'em fishing when they want to go with you. My 2 eldest Granddaughters (#3 only 2 months old) want to go this year, and while I'll fix them up with Zebcos & live bait, if they want to reel a fish in on the flyrod (that's IF their Daddy is there & IF I fish at all), I'll sure let the girls try...worse they can do is break a warranted rod/best they can do is have fun...that's a "no-brainer"!
Mike
FAOL..All about caring, sharing, & good friends!!