Passage 10.34.8
τὸν δὲ ἱερέα ἐκ παίδων αἱροῦνται τῶν ἀνήβων, πρόνοιαν ποιούμενοι πρότερον τῆς ἱερωσύνης ἐξήκειν οἱ τὸν χρόνον πρὶν ἢ ἡβῆσαι· ἱερᾶται δὲ ἔτη συνεχῆ πέντε, ἐν οἷς τήν τε ἄλλην δίαιταν ἔχει παρὰ τῇ θεῷ καὶ λουτρὰ αἱ ἀσάμινθοι κατὰ τρόπον εἰσὶν αὐτῷ τὸν ἀρχαῖον. τὸ δὲ ἄγαλμα ἐποίησαν μὲν καὶ τοῦτο οἱ Πολυκλέους παῖδες , ἔστι δὲ ἐσκευασμένον ὡς ἐς μάχην· καὶ ἐπείργασται τῇ ἀσπίδι τῶν Ἀθήνῃσι μίμημα ἐπὶ τῇ ἀσπίδι τῆς καλουμένης ὑπὸ Ἀθηναίων Παρθένου.
They choose the priest from among the boys who have not yet reached puberty, taking care beforehand that the period of priesthood shall expire before he attains maturity. He serves continuously as priest for five years, during which time he lives by the goddess according to a certain established way of life, and the bathing basins are provided for him in the ancient customary manner. This statue too was made by the sons of Polycleitus, and it is armored as though ready for battle. Furthermore, upon the shield has been crafted a relief imitating the design upon the shield of the image which the Athenians call the Parthenos.