At a campaign rally in Vermont on Tuesday and at three events in New Hampshire, including a town hall-style gathering in Portsmouth that drew roughly 600 people, older voters made up a sizable minority of the crowds.

Their visibility has been striking because Mr. Sanders’s unabashedly progressive message, calling for a “political revolution” to tax the rich and redistribute income, often appeals to idealistic young Americans who do not pay much in taxes. Even some of these older voters said they were a little surprised to be responding to the fiery, man-the-barricades exhortations of Mr. Sanders. But if young people and African-Americans identified with Barack Obama during his presidential run in 2008, older Americans said that Mr. Sanders had struck a deeply personal chord with them.

“I don’t think he’s too old — he’s articulate and on the ball,” said Leslie Dundon, 71, of Manchester, N.H. “And look, the older you get, the more you realize that life has actually taught you something, and you have something to contribute.”

Mr. Sanders, who is only starting to build a national campaign — he has hired a dozen staff members and raised about $4 million toward a $50 million goal over the next 10 months — said that support from older Americans was a central part of his strategy to win the Democratic nomination over the party’s front-runner, Hillary Rodham Clinton. A new survey by Quinnipiac University showed him moving up in the polls, with 15 percent support among Democratic voters, although polls at this point mainly reflect name recognition.