I vote you make them adults. For one, agreeing with everyone else that going for the 'strong, independent women' and 'secret agent' types, teenagers just aren't that. Teens are still trying to figure out who they are, what they want to be, what kind of personalities they have... There's a lot of development to be done.
The other reason I say to go for adults is this: I've read the Twilight saga. I've also read the House of Night saga by P.C. and Kristin Cast (http://www.amazon.com/Marked-House-Night-Novel-Novels/dp/0312360258/ref=sr_1_1?ie=UTF8&s=books&qid=1250481834&sr=1-1), as well as a couple out of The Chronicles of Vladimir Tod (http://www.amazon.com/Eighth-Grade-Bites-Chronicles-Vladimir/dp/0142411876/ref=sr_1_2?ie=UTF8&s=books&qid=1250482062&sr=1-2). All three series have one major thing in common, aside from the vampire theme: Main characters are all teenagers. It seems, from my own reading experience, that doing teenage vampires is...for lack of a better term, cliche. It would be more original, more unlike the vampire series that are already in existence, to have the vampires be adult characters.
no subject
The other reason I say to go for adults is this: I've read the Twilight saga. I've also read the House of Night saga by P.C. and Kristin Cast (http://www.amazon.com/Marked-House-Night-Novel-Novels/dp/0312360258/ref=sr_1_1?ie=UTF8&s=books&qid=1250481834&sr=1-1), as well as a couple out of The Chronicles of Vladimir Tod (http://www.amazon.com/Eighth-Grade-Bites-Chronicles-Vladimir/dp/0142411876/ref=sr_1_2?ie=UTF8&s=books&qid=1250482062&sr=1-2). All three series have one major thing in common, aside from the vampire theme: Main characters are all teenagers. It seems, from my own reading experience, that doing teenage vampires is...for lack of a better term, cliche. It would be more original, more unlike the vampire series that are already in existence, to have the vampires be adult characters.