Since then, the organization has funded trips to Israel for Jews between the ages of 18 and 26. The program has grown rapidly, from just over 9,000 participants in 2000 to roughly 48,000 participants this year, most of them Americans. Studies have shown that American Jews who visit Israel are less likely to marry someone of another religion and are more likely to feel closely tied to Israel and support the Israeli government.

Gidi Mark, the CEO of Birthright Israel, said the decision to offer trips to older Jews was spurred by a broader cultural shift, which has seen many young people delay major life decisions, like marriage.

“The decision-making time of young people about their future has moved over the years, from 25 or 26 to 30 or 32,” he said. “These are people we’d want to consider what Israel has to offer.”

At least for now, Mr. Mark said, the trips will also be free for 27- to 32-year-olds, although they will go in separate groups from the younger participants. He said the older participants could also establish “professional connections” with people in Israel that will remain useful once they go back home.

While the Jewish population in the U.S. is down from its high point of about 4% of the county’s overall population in the 1950s, it has in recent years stabilized at about 2%, according to the Pew Research Center. Intermarriage rates, however, have continued to climb: Between 2005 and 2013, a majority of Jews who tied the knot married a non-Jewish spouse. Young Jews also feel less emotionally attached to Israel than older Jews.

Though Birthright Israel has enjoyed broad support from within the American Jewish community—both orthodox Jewish organizations and gay and lesbian groups organize Birthright trips—not everyone agrees that raising the age limit is a good idea.

Robert Lappin, a Jewish philanthropist based outside Boston, has been pushing for several years to instead focus on getting younger Jews in their teens to go to Israel. He said he has encouraged Sheldon Adelson —the casino magnate and conservative political donor, who is also the largest donor to Birthright Israel—to support Birthright lowering the eligibility age to 16.

“I believe it’s a mistaken priority,” Mr. Lappin said. “When Birthright was started, the objective was to expose college-age kids to an Israel experience to enhance their Jewish identity and reduce intermarriage and assimilation.”