My DD got this for Christmas 2005 - she was just over 6 years old. She picked right up on it. Then again, everytime we went to a store that had one on display she would play with it so she had a pretty good feel for it.
The only thing she needed help with was setting it up initally - entering in her name, the dogs name, & saving the tricks they learned, etc. But that is stuff that is only done once. Once in a blue moon I'll play with them & they seem to be still pretty well taken care of. On a good note - if she doesn't play with it for a while, the dogs don't die - you just need to feed them & give them a bath & you're good to go.