is there any way you can get around cruise age requirements like maybe a notarized letter or something! can a 17year old go on a cruise with an 18 year old??

You must be 21 to cruise on Carnival, or have someone 25 older (parent or guardian) in the same cabin. There are exceptions, such as married couples under 21 (you must provide proof of marriage), and kids can be booked in a cabin by themselves, as long as the parents are on the cruise.