83 years old now in 2023 - what year born?

Today, 1 December 2023 if a person is 83 years old now, what year was he born? See below:

If 83 years old, year of birth is:
1939 or 1940*

*It depends on whether he was born before or after 1 January 1940.

If now 83 years and his year of birth 1939 if he was born after 1 December 1939 until 31 december 1939 inclusively, and his year of birth is 1940 if he was born from 1 January 1940 to 1 December 1940.

Other examples:

If now 10 years, year of birth 2012 or 2013
If now 14 years, year of birth 2008 or 2009
If now 21 years, year of birth 2001 or 2002
If now 60 years, year of birth 1962 or 1963

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