Chocolate for a 1 year old?

My son's 1st birthday is coming up and he hasn't had chocolate yet.  I'm thinking about getting a chocolate cake for his party, but for some reason I thought I heard that no chocolate before 1 because of allergy potential.  True or am I losing it?  (Also, he was premature, so on his birthday, his adjusted age will be 10.75 months old, if that makes sense.)