"When traveling with a minor and both parents/legal guardians are not cruising, we strongly recommend bringing an original signed letter from the absent parent/legal guardian authorizing the minor to travel with you. This will expedite processing by the Department of Homeland Security. Please note that a notarized letter to this effect is required if debarking with children in Mexico.
In addition to the above requirements, all guests 16 years of age or older must provide an official photo ID."
How long does it take to get a notarized letter? Your parents type up and print a letter naming at least one adult passenger on your booking as being responsible for you while on the cruise. You then find a Notary Public in your area/city/town and go to them and have them notarize the letter. They'll look at the document, ask for ID from your parents and possibly you, and then they'll stamp the letter with their official seal and atttest to it's authenticity. That's it. Just keep it with your cruise documents. Banks have Notaries Public. Law offices have them.