If the arrangement is
ABC or BAC
And
If they knew the questions asked and Anna was logical and so would realize the only way for no-one to be embarrassed and know the youngest at the same time is to ultimately keep silent. And Bob and Charlie too meaning they would realize that they need to state their information.
Then:
If ABC then A is the oldest and does not state this. B states C is not older than A and the configuration could be ABC, BAC, ACB for their minds. C states that C is not in the middle and the only possible configurations are ABC or BAC. This way they know C is the youngest however A and B’s position is not known.
Or
If BAC and they will know C is younger than A and is not in the middle. This reveals his position. Anna will keep silent and this means the arrangement can be BAC or ABC in their eyes.
Then
Zorro is a good logician.
Just to if Zorro is a not good logician if the youngest be:
BOB or ALICE because ACB means that they would work out A is the oldest if they were to work out B even if A doesn’t state her information- one has to know C is younger than A and in the middle to know B. For CAB there are insufficient clues for the position B. If BCA it has to be known that A is younger than C and C is in the middle but then they can deduce B is the oldest. Finally if CBA it means again A has to be known to be younger than C but still A’s position is not specified.