Are there any Cruise Lines that allow 18 yr olds to travel alone?

I want to go on a cruise with some friends, but I am the oldest (19) and the youngest is 18....most, you have to be 21....So, my question, is if we can travel alone without anyone over 21

Yes only one cruise line easycruise

http://info.easycruise.com/termsandConditionsV1.html

If you guys planing spring break cruise with this cruise line group 25 and ove call 1 888 516 6306.