The poll found that views have changed little since President Ronald Reagan signed a 1984 law that denied highway aid to states with lower ages. A Gallup survey a few weeks earlier found 79 percent in favor of raising the age, which had been lower to 18 in many states.
Gallup said substantial majorities in every subgroup believe the age should remain at 21. While those who describe themselves as liberal are more likely to favor a lower age, only 34 percent do so, compared to 18 percent of conservatives.
Regular drinkers are also more likely to support allowing young people to drink legally at 18. More than one-third, 35 percent, of those who reported having at least one drink a week favor a reduced age, compared to 29 percent of occasional drinkers and 18 percent of abstainers.
Gallup polls on the issue in 2001 and 2007 found young people were more likely to want the age reduced. But the most recent poll found they are in synch with their elders.
Many states cut the drinking age in the 1970s, following the argument that young people could vote, drive and serve in the military at that age. The 1984 bill was pushed to cut drunk-driving deaths, something studies suggest it achieved.
Gallup surveyed 1,013 adults between July 7 and July 10. The margin of error is 4 percentage points.