There are some cruise lines that allow 18 year olds to cruise without older supervision. Here is a list of the cruise lines and their age restrictions. You should check with the cruise line or your TA before booking to check that this information is correct. their rules change quite regularily and without warning. (Paragraphs 2 & 3 should apply to you)

"Guests Under 25 Years of Age

All cruise lines require that at least one person in each cabin meets a minimum age requirement. The information that follows was provided by the cruise lines at the time of this writing, is subject to change, and should be verified with your Vacations To Go cruise counselor prior to booking.

The lowest minimum age requirement for any cruise line is 18. The following cruise lines require that at least one person in each cabin is 18 or older: Cruise West, Cunard, Fred. Olsen Cruise Line, P&O Cruises, Peter Deilmann, Regent (Radisson) Seven Seas Cruises, SeaDream, Star Clippers, and Uniworld.

The following cruise lines require that either 1) All passengers in a cabin must be 18 or older, or 2) If anyone in the cabin is younger than 18 years old, someone in the cabin must be 21 or older: Disney Cruise Line, GAP Adventures, Paul Gauguin Cruises, Silversea and Viking River Cruises.

The following cruise lines require that at least one person in each cabin is 21 or older: Azamara, Celebrity, Costa (25 for March and April sailings), Crystal Cruises, Voyages of Discovery, Hurtigruten, MSC Cruises, Norwegian Cruise Line, Oceania, Princess Cruises, Royal Caribbean and Seabourn Cruise Line.

The following cruise lines require that either 1) All passengers in a cabin must be 21 or older, or 2) If anyone in the cabin is younger than 21 years old, someone in the cabin must be 25 or older: Carnival, Holland America and Windstar Cruises.

One exception to these age requirements is often made for underage married couples, who as long as they are both 18 are allowed to board unaccompanied. These couples may be asked to show proof of their marriage. This exception is based on individual cruise line policy.

Your age on the date of sailing is generally considered your age for the length of the cruise."
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