Question: A man was born on January 1st, 23 B.C. and died January 2nd, 23 A.D. How old did he live to be?
Answer: 45 years old.
There is no year 0 so you can add 23 to 23 but you must subtract one to take year 0 out of consideration: 23 + 23 - 1 = 45 years old. In some cultures people are born 1 years old, in this case they would be 46 years old when they die.