Adam Clarke on Acts 21:16

And brought with them one Mnason, etc. - It is not very likely that they would bring a man with them with whom they were to lodge in Jerusalem; therefore, the text should perhaps be read as Bp. Patrick proposes: There went with us certain of the disciples of Caesarea, bringing us to one Mnason, with whom we were to lodge. This is most likely, as the text will bear this translation. But it is possible that Mnason, formerly of Cyprus, now an inhabitant of Jerusalem, might have been down at Caesarea, met the disciples, and invited them to lodge with him while they were at Jerusalem; and, having transacted his business at Caesarea, might now accompany them to Jerusalem. His being an old disciple may either refer to his having been a very early convert, probably one of those on the day of pentecost, or to his being now an old man.