He told me that voters and journalists ask him about his age more often than they do about his sexual orientation. (If elected, he’d be the first openly gay president.)

So we spent most of a nearly hourlong car ride between campaign stops in the New York City area talking about it. He conceded that the longer you’re alive, “the more you learn,” and that there are lessons and life passages still in the offing for him. He’d like to be a parent, but if he succeeds on his current quest, he’d become the leader of the free world first.

“A lot of things in my life have been out of sequence,” he said. “I was a mayor before I got married. I was a war veteran before I had dated.” He was referring to his seven months in Afghanistan and recognizing that while he has been precociously ahead of the game in many regards, he was behind in others. It was only four years ago, at 33, that he finally had a serious romantic relationship — with the man, Chasten, who is now his husband.

Age has played out in surprising ways in the Democratic primary. While Buttigieg is unusually young, the other three candidates grouped with him at the head of the pack — Joe Biden, 77; Elizabeth Warren, 70; and Bernie Sanders, 78 — are unusually old. Sanders had a heart attack in October, and Biden’s energy has visibly dimmed, to a point where some of his aides and supporters have sought to reassure voters by whispering about the possibility that he’d want to serve just one term.

The oldest candidate, Sanders, is by far the most popular among the youngest Democratic voters, getting the support of 52 percent of those between the ages of 18 and 34 in a national Quinnipiac poll released on Tuesday. Buttigieg got just 2 percent of that group, in contrast with 12 percent of Democratic voters between 35 and 49, 12 percent of those between 50 and 64 and 11 percent of those 65 and older. He attributed that to younger voters’ attraction to Sanders’s less pragmatic, more ideologically pure vision.