Ancient Roman criminals had almost unlimited power because there were in fact no policemen. Since full army units were forbidden in Italy, only a limited number of legionnaires were available to maintain order. Street gangs actually kept the peace, within the boundaries of their respective territories.
Caesar's choice of Vorenus as a magistrate actually makes sense. Having served in the legion as a prefect, Vorenus has experience as an administrator. The transition to civil service would not be difficult.
Lindsay Duncan was 54 years old at the time of her shooting her nude scene.