Never heard anyone ask that question before, its a dangerous zone because you can always say its age descrimination if you do not get the job. Doesn't really matter when you're 30, but if you're 55 and someone asks you that, one can get pretty offended.

Wow, this is not an appropriate question! The only thing close to that which i've heard is "when did you graduate from grad school"

Very inappropriate indeed. If you are a female candidate, it is doubly inappropriate as it's rude to ask a lady her age.