The idea is that this person would have a broad knowledge coupled with domain specific expertise. These people are curious about the world and because of their broad knowledge they can communicate across discipline. This makes for collaborati teams.
As a parent age appropriate never works for me and that is true of many children. I would love to see it done using stages of development instead.
One of the things I have found is people are willing to help if you ask. In our co-op the kids were really interested in cosmology and we contacted the university and they sent us a list of grad students who would tutor them. The guide book should have some hints on how to connect with experts. Sometimes it is as simple as picking up the phone.