It's a fabulous ship with lots to do. Beautiful, wonderful...I seriously could go on for days...
As far as the 19 year old, Carnival doesn't offer programs per say for that age group other than what any other adult can do. And traveling when you are, there may or may not be a lot of other teens on board. But the cruise will be what they make of it, and they should have a good time no matter whom else they meet on board-they should meet someone close to their age.
They do have a sushi bar, but not sure about a chinese buffet...can't remember.
Have a great trip.