Pausanias 7.24.4 (tr. W.H.S. Jones):
In a more remote age there was chosen to be priest for Zeus from the boys he who won the prize for beauty. When his beard began to grow the honor for beauty passed to another boy. Such were the customs.
τὰ δὲ ἔτι παλαιότερα προεκέκριτο ἐκ τῶν παίδων ἱερᾶσθαι τῷ Διὶ ὁ νικῶν κάλλει· ἀρχομένων δὲ αὐτῷ γενείων ἐς ἄλλον παῖδα ἡ ἐπὶ τῷ κάλλει μετῄει τιμή. ταῦτα μὲν οὕτως ἐνομίζετο.
The following custom is, to my knowledge, still carried out in Thebes. A boy of noble family, who is himself both handsome and strong, is chosen priest of Ismenian Apollo for a year.
τόδε γε καὶ ἐς ἐμὲ ἔτι γινόμενον οἶδα ἐν Θήβαις· τῷ Ἀπόλλωνι τῷ Ἰσμηνίῳ παῖδα οἴκου τε δοκίμου καὶ αὐτὸν εὖ μὲν εἴδους, εὖ δὲ ἔχοντα καὶ ῥώμης, ἱερέα ἐνιαύσιον ποιοῦσιν.