Damon's parents never cared about birthday's, so he never did know his birthday. If anything they wanted to do an abortion, but they would have to have lots of money to do so. So when he was born the parents didn't care and just saw him as another thing, a worthless leech that they can tell what to do when he gets older and can hurt. That was if he was in the house. His parents didn't care unless he did something wrong such as not getting good grades or if he was blamed for something he didn't do, but they don't know that. In fact for now he was still a baby which ment people could see if they treat him badly and he'd be sent somewhere else and the parents would go to prison. They can't hurt him...yet...