John Lightfoot on Matthew 24:34

[This generation shall not pass, &c.] Hence it appears plain enough, that the foregoing verses are not to be understood of the last judgment, but, as we said, of the destruction of Jerusalem. There were some among the disciples (particularly John), who lived to see these things come to pass. With Matthew 16:28, compare John 21:22. And there were some Rabbins alive at the time when Christ spoke these things, that lived till the city was destroyed, viz. Rabban Simeon, who perished with the city, R. Jochanan Ben Zaccai, who outlived it, R. Zadoch, R. Ismael, and others.