43 years old now in 2023 - what year born?

Today, 1 December 2023 if a person is 43 years old now, what year was he born? See below:

If 43 years old, year of birth is:
1979 or 1980*

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

If now 43 years and his year of birth 1979 if he was born after 1 December 1979 until 31 december 1979 inclusively, and his year of birth is 1980 if he was born from 1 January 1980 to 1 December 1980.

Other examples:

If now 12 years, year of birth 2010 or 2011
If now 18 years, year of birth 2004 or 2005
If now 29 years, year of birth 1993 or 1994
If now 78 years, year of birth 1944 or 1945

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