Passage 10.28.2
ἐπηκολούθησε δὲ ὁ Πολύγνωτος ἐμοὶ δοκεῖν ποιήσει Μινυάδι· ἔστι γὰρ δὴ ἐν τῇ Μινυάδι ἐς Θησέα ἔχοντα καὶ Πειρίθουν ἔνθʼ ἤτοι νέα μὲν νεκυάμβατον, ἣν ὁ γεραιός πορθμεὺς ἦγε Χάρων, οὐκ ἔλαβον ἔνδοθεν ὅρμου. Minyad, an unknown work. ἐπὶ τούτῳ οὖν καὶ Πολύγνωτος γέροντα ἔγραψεν ἤδη τῇ ἡλικίᾳ τὸν Χάρωνα.
In my opinion, Polygnotus followed the account given in the Minyad; for indeed, there is a scene depicted in the Minyad showing Theseus and Peirithous, where the ship prepared for the transportation of the dead, guided by the aged ferryman Charon, was newly built and not yet received into its anchorage. Therefore, Polygnotus also portrayed Charon as a man already advanced in years.