333 Months

I have never understood why babies go by a different age system then everybody else. When a baby is born they are never a certain amount of years old, they go by months. Babies are never half a year old or 1 and a half years, they are six months or eighteen months old. Then suddenly at around 2 years old, they stop going by months. Why? Can people not count higher than 24? I think if babies are going to go by months then we all should. So everybody send me presents, because tomorrow I will be the big 333 months old. Yay me!