cantina (kàn-tê´ne) noun
A bar that serves liquor.
[Spanish, canteen, from Italian, wine cellar.]
The direct translation isn't really the best thing to go by.
People under 21 are allowed in a lot of establishments that serve alcohol. Most Irish and English pubs, even the the US, for instance, allow all ages. In a lot of cases, Cantina and Canteen is used to describe a restaurant. But in the case of the Cana Bar, which I went to last year, it is the ONLY thing they serve, so understandably they would not allow people under 21.