On the vast majority of cruise lines, you cannot gamble in the ship's casino if you are only 20 years old, as the industry standard for gambling in international waters is typically 18 or 21, with a strong lean toward 21 for U.S.-based sailings. Major lines like Royal Caribbean, Celebrity, and Carnival generally set the gambling age at 18 for most international and Caribbean itineraries. However, if the ship is sailing in specific regions—most notably Alaska—the minimum age for gambling (and drinking) is strictly raised to 21 to comply with local and state regulations. Additionally, some cruise lines that cater to a more adult or premium market may set a blanket age of 21 for all casino activities regardless of the route. It is essential to check the specific "Guest Conduct Policy" for your chosen cruise line and itinerary, as the ship's casino management will frequently request a government-issued photo ID or your SeaPass card to verify your age before allowing you to play at the tables or slots.