I might wait to take a six year old. My general reasoning:
It's several miles (3 or 3.5 if I remember correctly) at a pretty quick pace.
The information presented is completely family safe, however, not told in a "kid friendly" way (that is, it's not necessarily peppy or vocally animated).
Our tour didn't have a lot of on-the-go "why" question time, so there may be a moment for a question or two, but not enough to satisfy the questions my 6yo grandsons would come up with!
There's a lot of time spent just imagining Walt being at any place, while listening to a recorded narration.
There's no guarantee of specific rides.
Our tour had a 9yo and 14yo who both claimed to be huge Walt Disney fans, and they were begging to be done with the tour by the water break... Which affected the rest of the tour as they whined their way through the next 90 minutes. It's Disneyland, and kids get over stimulated, I get it. But I'm still a bit salty about it, obviously, and it has made me second-guess what age I would bring a child on a tour that's pretty adult-activity focussed.