Are there any vacational cruise lines that allow people 18 and over to travel alone?

A group of friends and I want to plan a cruise and we are all 19... However, most cruise lines require people under 21 to travel with someone who is over the age of 25... Are there any cruise ships that travel to the Caribbean's that will allow my friends and I to travel alone?

princess cruise does...but i dont know about drinking...im booking a cruise for me and my gf...we are 19-18. but i want to make sure i can lay out in the sun with a cocktial or have a few during the night....

The requirements are actually a little different than you stated. Carnival Cruise Line requires at least one person in each cabin be age 25 or older. All of the other cruise lines, except Cunard, requires at least one person age 21 or older in each cabin. So, unless you go on Cunard (it does mostly Trans-Atlantic and a few Caribbean) you WILL need to find a friend who is at least 21 to go with you.

That applies to Princess, Royal Caribbean, Holland America, Norwegian and Celebrity. There are, however, exceptions to this for married couples and proof of marriage must be provided.