A year after a record surge of young voters helped drive Mayor Zohran Mamdani to victory, turnout appears to be snapping back into a more typical pattern, as New York City voters decide a series of combative Democratic primaries.

About 172,000 people cast their ballots during this year’s early in-person voting period, which ended on Sunday. That was a sharp but expected drop from the nearly 400,000 voters who turned out during the same period in 2025 when Mr. Mamdani was on the ballot in a high-profile mayoral race against Andrew Cuomo.

In a more notable shift, the early voters were markedly older, with the average age of voters rising by a full decade — to 57 from 47 — compared with early voting last year.

Those trends may not carry over to the overall electorate as Primary Day votes pour in on Tuesday. For now, though, the turnout and average age are a cause for concern for Mr. Mamdani and some of the leftist candidates he has campaigned for in competitive races for congressional and state legislative seats.

Few expected truly high turnout for these primaries. There are no major citywide or statewide contests at the top of the ballot, and some parts of the city do not have competitive contests at any level.

Still, the Democratic Socialists of America, a group that helped Mr. Mamdani win last year, was concerned enough about the decline of young voters to convene an emergency meeting last week to try to correct course. (The share of younger voters did increase toward the end of the early voting period, following a typical turnout pattern.)

Mr. Mamdani’s 2025 success rested, at least in part, on bringing out new voters. Polls also suggest that younger voters are far more likely than their older counterparts to support Mr. Mamdani and the candidates he is backing.

Overall, the share of the early vote electorate younger than 40 declined from 40 percent last year to 28 percent this year. Voters 60 or older, meanwhile, accounted for 46 percent of the early vote, up from 34 percent last year.

Turnout trends have varied somewhat by district.

In the Seventh Congressional District, one of the country’s youngest and most progressive districts, an open seat was created when Representative Nydia Velázquez announced her retirement. The age of the median voter in the race to succeed her increased by about four years from this point in 2025 and was considerably younger than it was in August 2022, when the district had a midterm primary that was not considered competitive. Turnout in the district that spans parts of Brooklyn and Queens is down by about half compared with last year.

Mr. Mamdani has endorsed Claire Valdez, a state lawmaker and fellow member of the Democratic Socialists of America, and he spent the weekend campaigning with her in neighborhoods where they want to increase turnout. She is facing Antonio Reynoso, the progressive Brooklyn borough president, who has explicitly targeted older voters who live in the district.

In New York’s 10th Congressional District, Brad Lander, the former city comptroller and mayoral candidate, is hoping to unseat Representative Daniel Goldman with Mr. Mamdani’s backing.

Turnout in that race is about half of what it was in 2025, but nearly twice as many people have voted early as did in August 2022, the last time the district saw a competitive primary. The median age of early voters there — 52 — is between those of the 2022 and 2025 cycles.

Mr. Mamdani has not endorsed a candidate in the race for New York’s 12th Congressional District, where Representative Jerrold Nadler is retiring after three decades. The district, which encompasses most of central Manhattan, is among the most civically engaged in the country and has seen the highest overall turnout and median voter age of any in the city.

Polls suggest the race is a dead heat between two state assemblymen, Micah Lasher and Alex Bores. Both campaigns generally expect Mr. Lasher to do better among older voters and Mr. Bores among younger ones. (Jack Schlossberg, John F. Kennedy’s grandson; and George T. Conway III, an anti-Trump lawyer, are also in the race.)

Just to the north, in the 13th Congressional District, overall turnout declined less precipitously in early voting. Residents of the Upper Manhattan- and Bronx-based district have voted at about two-thirds the rate they did this time last year. The median voter age increased to 58 from 50, but is still lower than in 2022.

That primary appears to be competitive based on recent polling. Representative Adriano Espaillat, a Democrat and the chairman of the Congressional Hispanic Caucus, is trying to fend off a challenge from Darializa Avila Chevalier, a democratic socialist backed by Mr. Mamdani. She is generally expected to benefit from younger turnout.

If past elections are any guide, most voters in the contests have yet to be accounted for. In last year’s Democratic primary, early in-person voting accounted for about 35 percent of the total vote. In 2022, it was just 22 percent.

Saurabh Datar and Alex Lemonides contributed reporting.