21-year-olds do wear watches... don't worry about that. Popular watches that aren't too pricey (majority are under $100) are Fossil brand watches. They have great designs, and good warranties. If you're looking for something a little more elegant or more expensive, I would agree that Gucci, Chanel, Dolce and Gabbana are good ideas. Other good brands are Tag Heuer, Swatch (they're not just the colorful plastic watches we wore in the eighties, now they have really nice stuff!) and there's always classics like Cartier, Rolex, and Movado. If you're still unsure, take her watch shopping with you, or even give her a gift certificate to a store like Macy's that has lots of different brands and styles. Anything you give her, I'm sure she'll love!