On which cruise lines may you have your own stateroom at 18?

Question

I know a lot of them are 21..or even older sometimes

Answer 1

you can't travel alone if you are under age 25. (if you are in american waters)

cruiseclues.com

Answer 2

No cruiseline sailing from American ports permit you to travel alone if you are under 25.  If you are NOT 25 years old, you must share a cabin with someone who is at least that age - and that person must be a guardian or parent.

Answer 3

Don't think there are any - unless you're a married couple.