Another interesting tradition, that would mean the opposite of those that assert Luke was a Gentile, is that Luke was one of the seventy (Luke 10:1ff). To me, Luke 1:2 seems to discount this tradition....Luke was not a disciple or one of the twelve...
Epiphanius of Salamis (ca. AD 315-403) wrote that the third gospel was by Luke, and that Luke was one of the seventy(two).
Such can also be found in Pseudo-Hippolytus (lost and found, so probably hard to date), some others said the same, including Dialogue on the True Faith of God.ἔφασκον δὲ ὅτι ἰδοὺ τρίτον εὐαγγέλιον τὸ κατὰ Λουκᾶν. τοῦτο γὰρ ἐπετράπη τῷ Λουκᾷ, ὄντι καὶ αὐτῷ ἀπὸ τῶν ἑβδομήκοντα δύο τῶν διασκορπισθέντων ἐπὶ τῷ τοῦ σωτῆρος λόγῳ, διὰ δὲ Παύλου τοῦ ἁγίου πάλιν ἐπανακάμψαντι πρὸς τὸν κύριον ἐπιτραπέντι τε αὐτοῦ κηρῦξαι τὸ εὐαγγέλιον. (Panarion 51.11)
I am not buying stock in this tradition, just relaying that it exists.