“ Castro kind of comes off with fangs every now and again, as he did with Biden and Beto — Buttigieg just doesn’t do that,” he said, a reference to Julián Castro’s debate-stage attacks, which backfired. “I think that probably appeals to older Iowans’ sense of decorum.”

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In a brief interview before an event in Storm Lake on Tuesday, Mr. Buttigieg theorized that he was attracting older Americans because they might have “a more generous understanding of what experience means.”

“Every older person was a younger person once,” he said. “And maybe it demystifies a little bit the extent to which age represents readiness.”

At the same time, Mr. Buttigieg is struggling to attract voters on the opposite end of the spectrum — those closer to his own age. At all of his events in Iowa, even the rally in Council Bluffs, which was held at a high school, older people made up a sizable portion of Mr. Buttigieg’s crowds, providing a striking contrast: a fresh-faced mayor of a midsize city speaking to silver-haired attendees.

Asked in the interview why he was having more trouble connecting with younger voters, he pointed to their “strong sense of impatience about the changes that need to come and the extent to which it feels like they’ve grown up in an America that just tolerates the intolerable.” But he said he was also working to convince young people to come around to his more tempered vision for change.

“The case I’m making is that my proposals are plenty big,” he said.

Older voters who support Mr. Buttigieg say he represents the best hope for the country, offering a future-focused vision that they feel will help younger generations. They often cite his intelligence, his plain-spokenness and his military service as reasons he is now a top choice even if they knew little of him just months earlier. And of those who mention his sexuality at all, they often treat it with a shrug.