Alcohol law is one of the most variable things on earth, so never assume your home rules travel with you. Drinking ages range from sixteen in parts of Europe to twenty-one in several countries, and a handful of nations ban alcohol outright or permit it only to non-Muslims with licenses, notably in parts of the Gulf and South Asia. Even within one country rules shift: several Indian states are fully dry, some US and Nordic jurisdictions restrict sales to state shops or certain hours, and many countries ban sales during elections or religious holidays.
Public consumption is its own minefield. Drinking openly in streets and parks is normal in some European countries, fined in others, and can mean arrest in stricter ones; public drunkenness is treated harshly in several places even where drinking itself is legal. Import limits also apply at borders, typically a liter or two duty-free, and bringing alcohol into dry jurisdictions can be a criminal offence.
The stakes are highest where you least expect them, so a two-minute check of your destination's embassy or official tourism guidance before flying is genuinely worth it. When on the ground, follow the local crowd's behavior and keep drinking to licensed venues in any conservative country.