The Passenger Type field can be accessed in the Itinerary > Clients Tab > Details Subtab > Passengers grid. This field is designed to help with categorizing Passenger Types in Group itineraries and can be used in conjunction with the existing Age-group field.
Passenger Type setup
Define Passenger Types under Tools > Setup > General lists > Passenger Type.
To include the Passenger Type field in booking emails to suppliers e.g. on Rooming Lists, please see this help file.