Neither. My birthday is in March. Beginning of January, I'm already saying I am the age I will be in March. I don't know why, but I've been doing it since high school.
@Serenitree Lol, I was born on Jan 1, and I start getting birthday calls midnight Dec 31. People ask “were you the 1st baby ?” I always reply that I was practically the last one that day—11:07 pm. 😅