47 years old now in 2023 - what year born?

Today, 7 December 2023 if a person is 47 years old now, what year was he born? See below:

If 47 years old, year of birth is:
1975 or 1976*

*It depends on whether he was born before or after 1 January 1976.

If now 47 years and his year of birth 1975 if he was born after 7 December 1975 until 31 december 1975 inclusively, and his year of birth is 1976 if he was born from 1 January 1976 to 7 December 1976.

Other examples:

If now 7 years, year of birth 2015 or 2016
If now 13 years, year of birth 2009 or 2010
If now 21 years, year of birth 2001 or 2002
If now 31 years, year of birth 1991 or 1992

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