Former Maryland Gov. Martin O'Malley made an apparent joke about his opponents' ages at Saturday night's debate — and the crowd at Saint Anselm College booed him for it.

As Independent Vermont Sen. Bernie Sanders finished answering a question about the U.S. strategy in Syria, O'Malley cut in, asking the moderators: "May I offer a different generation's perspective on this?"

Some in the crowd booed in response.

Sanders is 74 years old, and former Secretary of State Hillary Clinton is 68. O'Malley is 52.