One should never Thou-Thee their elders, while addressing them, nor take their names. Thou-,thee-,ing, or taking of names, is only allowable in addressing inferiors or one's compeers.
त्वंकारं नामधेयं च ज्येष्ठानां परिवर्जयेत्। अवराणां समानानामुभयेषां न दुष्यति॥