Jack Schlossberg, the grandson of John F. Kennedy, has built his campaign for a New York City House seat around turning the page on the Democrats’ old guard.

Yet when he debuts his first paid advertisement on Wednesday, the 33-year-old candidate has chosen his party’s oldest living leader, Representative Nancy Pelosi of California, to do the talking.

The choice reflects the unique challenge Mr. Schlossberg faces ahead of a marquee June primary against more seasoned rivals. He may have star power and youth, but he is still trying to persuade aging voters who form the Democratic base that he is serious and experienced enough to represent a storied Manhattan district — home to corporate chieftains, media empires and cultural meccas.

The 30-second ad, which was shared first with The New York Times, uses Ms. Pelosi, a former House speaker, to make his case. In it, the congresswoman, 86, speaks directly to the camera to say that Mr. Schlossberg has “a deep sense of duty” and the kind of energy that could help propel Democrats back to power nationally.

“This moment calls for leaders who understand the stakes and how to deliver for the people they serve,” she says, sometimes over clips of him campaigning. “Jack Schlossberg is that kind of leader.”

Mr. Schlossberg is among the first candidates in New York’s 12th District to start spending on paid media. But a handful of super PACs funded by competing A.I. companies and former Mayor Michael R. Bloomberg have already burned through millions of dollars trying to sway voters toward or away from his rivals.

Mr. Schlossberg’s outlay will be relatively modest in comparison. The campaign said it would initially spend $70,000 on digital platforms, and eventually add more digital spending and $250,000 in broadcast TV time — a relatively small sum in the nation’s most expensive media market.

Mr. Schlossberg, who has reported inherited assets between $10 million and $32 million, said he would not be spending any of his own money in the race. He does not have a super PAC behind him.

While there has been no real public polling to date, private polls released by several of Mr. Schlossberg’s rivals have all narrowly put him in the lead.

With two months left until Primary Day, two state assemblymen — Alex Bores and Micah Lasher — are not far behind; followed by George Conway, a former Republican turned high-profile antagonist of President Trump, and Nina Schwalbe, a public health expert. Because the seat is safely Democratic, the primary winner will almost certainly win the general election to replace Representative Jerrold Nadler, who is retiring.

Mr. Schlossberg, earlier known for a head-turning social media presence, has largely tried to portray his opponents as old-fashioned, risk-averse establishment figures who have not been able to check Mr. Trump. They, in turn, have raised doubts about the thinness of his résumé, which includes no long-term traditional work experience, elected or otherwise.

In an interview, Mr. Schlossberg said it was an obvious choice to turn to Ms. Pelosi, who is perhaps her party’s most respected elder stateswoman.

“Speaker Pelosi is the backbone of our party,” he said. “She most importantly understands better than anyone how the House of Representatives works and what the Democratic Party needs right now.”

Yet embracing Ms. Pelosi may also have its costs, complicating Mr. Schlossberg’s attempts to position himself as an outsider and a fresh face by reminding voters of his family’s deep ties to the Democratic establishment.

Mr. Schlossberg said he believes he first met Ms. Pelosi when he was in high school. Alongside his family, he presented her with the John F. Kennedy Profile in Courage Award in 2019.

The candidate said Ms. Pelosi asked to meet with him in her Washington office before she endorsed his campaign in February.

“I printed out all my plans I have for the district and the country,” he said. “She read them over and quizzed me.”

An earlier version of the ad shared with The Times included footage of Mr. Schlossberg and Ms. Pelosi spending time with his mother, the former ambassador Caroline Kennedy, and his niece, the daughter of his sister Tatiana Schlossberg. (Ms. Schlossberg, who was an environmental journalist, died in December after a fight with blood cancer that she chronicled in a widely read essay.) That footage was cut from the final ad before it was distributed.

In the interview, Mr. Schlossberg said he exempted Ms. Pelosi from his critique of this party’s aging officials — and argued voters would, too.

“I put her in a category of her own,” he said. “She has magic that doesn’t age. It wins.”