Yeah, Trump was 70 when elected, the oldest ever for a first-timer( Reagan was 74 when re-elected). Sanders, if elected, would be 79 on taking office. That's asking a heck of a lot at that age, physically and mentally, even if you keep yourself in good shape. The stress of the campaign is only for openers, what follows would make that look like a walk in the park. Should he choose to run, his choice of running mate might decide the election.  So much speculation...