The day before yesterday I was 25 and the next year I will be 28. This is true only one day in a year.
What day is my birthday?
Your birthday is on December 31.
Today is January 1st and the day before yesterday is December 30.
So, the day before yesterday, you were 25. Yesterday, you turned 26. This year, you will turn 27 and next year, you will turn 28.