y'know, thats a situation i wouldn't mind being in....
I say go for both. Take one out one night, and the other out the next. Just don't forget which one is called what.
That way you can find out what the younger girl is like and still have the older one as a backup

Of course, one little mistake and...
Or if they get a chance to talk...
Or if a co-worker blabs off to one of them...
hmmm, maybe not such a good idea. You have to either try to be a player (not looking good in your situation) or choose one over the other (not a pleasant choice, and serious ramifications either way you go.)
Dude, you are in a jam. Only way i could help you further is if I saw them both. Then I could help you choose. Other than that you gotta pick. Or neither, that's allways a choice...
Your call.