If you book two cabins, remember that at least one adult needs to share a room with the minor.
For first time cruisers, maybe something less exotic like the Caribbean might make you feel more comfortable.
RCI Radiance of the Seas Sep 2009
NCL Sun March 2008
Carnival Destiny June 2006
Carnival Ecstasy June 2002
Carnival Elation August 2000
Celebrity Century June 1998
Carnival Carnivale August 1993