Find Your Cruise
Well here in uk is 18 or 21 pubs nightclubs is 21 even some super markets its 2.
From FAQ's on Costacruises.com
Alcohol purchased in the gift shop or onshore will be held for you until disembarkation. No alcohol may be brought onboard at embarkation. Minimum drinking age onboard is 21 and you must be 21 as of the sailing date.