99 years old now in 2023 - what year born?

Today, 7 December 2023 if a person is 99 years old now, what year was he born? See below:

If 99 years old, year of birth is:
1923 or 1924*

*It depends on whether he was born before or after 1 January 1924.

If now 99 years and his year of birth 1923 if he was born after 7 December 1923 until 31 december 1923 inclusively, and his year of birth is 1924 if he was born from 1 January 1924 to 7 December 1924.

Other examples:

If now 4 years, year of birth 2018 or 2019
If now 17 years, year of birth 2005 or 2006
If now 23 years, year of birth 1999 or 2000
If now 52 years, year of birth 1970 or 1971

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