In my research, I've found that Zohran Mamdani's overall wins amongst a variety of demographics, including youth voters, launched his victory in the Mayoral election.
Mamdani himself has not analyzed the demographics that won his election. When reading through his post-win speech, he did not outright identify who his audience is, something that seems to be very common with politicians. That being said, he did stress themes and figures of speech that are very popular among younger voters that are just breaking into politics.
Here are the places I read the transcript of his speech:
https://www.theguardian.com/us-news/2025/nov/05/zohran-mamdani-victory-speech-transcript
https://www.nytimes.com/interactive/2025/11/09/nyregion/zohran-mamdani-nyc-mayoral-speech.html
For secondary sources, I found a NYT article that analyzed the groups responsible for the main coalition of Mamdani's voter base, including immigrant, POC, and younger voters in droves. The wording used by NYT stressed the high participation in the election, saying "young voters turned out in droves." They analyzed that younger voters as a demographic had the highest percentage of support and votes for Mamdani over any other group. As well, the NYT analyzed the impact of the Black communities that voted for Mamdani, citing their votes as integral to his win.
"The Demographic Trends that Shaped Mamdani's Win," by Maya King, et. al
https://www.nytimes.com/2025/11/11/us/mamdani-nyc-voters-election-demographics.html
As well, NPR stated that youth turnout was the highest of any demographic in this election, supporting many of the claims made by the NYT.
"Mamdani's youth support goes beyond New York..." by Elena Moore,
https://www.npr.org/2025/11/02/nx-s1-5531004/zohran-mamdani-new-york-young-voters
My sources are all fairly reliable, being old, transparent news sources that all cite their financial support and interests. All information about them is very publicly accessible. However, there is always a potential for bias within a publication and from the writing of individual reporters.
This claim seems pretty accurate. Youth support was documented as having turned out substantially, being a demographic that historically has been hard to rouse within political voting cycles. The only thing I could think of that undermines this claim is not including other demographics that helped Mamdani win the election: Black voters, renters in New York, South Asians/Muslims.