42 years old now in 2023 - what year born?

Today, 1 December 2023 if a person is 42 years old now, what year was he born? See below:

If 42 years old, year of birth is:
1980 or 1981*

*It depends on whether he was born before or after 1 January 1981.

If now 42 years and his year of birth 1980 if he was born after 1 December 1980 until 31 december 1980 inclusively, and his year of birth is 1981 if he was born from 1 January 1981 to 1 December 1981.

Other examples:

If now 9 years, year of birth 2013 or 2014
If now 14 years, year of birth 2008 or 2009
If now 30 years, year of birth 1992 or 1993
If now 33 years, year of birth 1989 or 1990

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