Cruise ships follow a complex blend of "Flag State" laws and "Port of Call" regulations. While in international waters, ships generally follow the laws of the country where they are registered (the "Flag State"). However, most major lines (Royal Caribbean, Carnival, etc.) set a standard minimum drinking age of 21 for all sailings departing from North America. For cruises departing from Europe, South America, or Australia, where the legal age is lower, the drinking age often drops to 18. When the ship is docked in a port of call, it must strictly adhere to the local laws of that country. For example, if a ship is docked in Cozumel, the drinking age on board may temporarily align with Mexico's age of 18. Furthermore, many cruise lines allow parents to sign a waiver for children aged 18–20 to consume beer or wine only on specific international itineraries. Always check the specific "Guest Conduct Policy" for your 2026 sailing, as these rules are strictly enforced by onboard security.