I think it depends on the child and that's why it would just be a height restriction. As far as I know Disney has never done an age restriction on a ride.Depending on the intensity of the ride, 7 (or very tall 6) may be too young for some kids to go alone. I find it hard to believe that Disney would be ok with letting kids that young go unattended on a ride like this, but who knows? Maybe I'm just overprotective
Don't Banshees have a double set of wings? It is hard to make out in the picture if it is all coming from the same vehicle or more than one....

This photo shows only one set but in other photos of them flying they have a part of their wing that could appear to be a second wing but it is not.