What ship are you going on? Most of the summer cruise ships have great programs. The teen programs are from ages 13 to 17. If you are 10 or 11 or 12 they have another age group for you, it's pretty grown-up and has some of the same stuff the teens do.
There are lots of kids on board but some ships have more than others. But still you have some privacy, too. And I have cruised before and done some of the activities that aren't just for kids, like mini-golf and ballroom dance and flower arrangeing. The French islands are Martinique and St.Martin. They speak french there. But they are NOT primitve. kind of old-fashion.