100 years old now in 2022 - what year born?

Today, 5 December 2022 if a person is 100 years old now, what year was he born? See below:

If 100 years old, year of birth is:
1921 or 1922*

*It depends on whether he was born before or after 1 January 1922.

If now 100 years and his year of birth 1921 if he was born after 5 December 1921 until 31 december 1921 inclusively, and his year of birth is 1922 if he was born from 1 January 1922 to 5 December 1922.

Other examples:

If now 4 years, year of birth 2017 or 2018
If now 17 years, year of birth 2004 or 2005
If now 18 years, year of birth 2003 or 2004
If now 57 years, year of birth 1964 or 1965

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