I waited until after the one year mark. Lilah actually LOVES superdark chocolate (like the 70%+ cocoa content kind-- she has good taste!). For those with a family history of food allergies, I think the recommendation is to wait till age two on chocolate, otherwise, wait till one year.
I made a carrot cake for Lilah's first birthday; I didn't want to leave out all the other kids who were not yet a year old at her party, plus I figured it was the first time ever she was having cake at all; it didn't need to be chocolate on top of that.