81 years old now in 2023 - what year born?

Today, 7 December 2023 if a person is 81 years old now, what year was he born? See below:

If 81 years old, year of birth is:
1941 or 1942*

*It depends on whether he was born before or after 1 January 1942.

If now 81 years and his year of birth 1941 if he was born after 7 December 1941 until 31 december 1941 inclusively, and his year of birth is 1942 if he was born from 1 January 1942 to 7 December 1942.

Other examples:

If now 10 years, year of birth 2012 or 2013
If now 16 years, year of birth 2006 or 2007
If now 19 years, year of birth 2003 or 2004
If now 31 years, year of birth 1991 or 1992

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