42 years old now in 2022 - what year born?

Today, 6 December 2022 if a person is 42 years old now, what year was he born? See below:

If 42 years old, year of birth is:
1979 or 1980*

*It depends on whether he was born before or after 1 January 1980.

If now 42 years and his year of birth 1979 if he was born after 6 December 1979 until 31 december 1979 inclusively, and his year of birth is 1980 if he was born from 1 January 1980 to 6 December 1980.

Other examples:

If now 6 years, year of birth 2015 or 2016
If now 18 years, year of birth 2003 or 2004
If now 29 years, year of birth 1992 or 1993
If now 83 years, year of birth 1938 or 1939

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