I'm 14 and my sister is 17. We LOOOOVE the cd and have listened to it w/ my parents in the car. Its a little embarrassing but I love the music. We have seen Cabaret and Rent so i dont think its a big deal.
Maybe 5 years ago Avenue Q would be inappropriate for 14 year olds, but I think things have changed. They should have it banned for certain ages, but for teens it should be ok.