102 years old now in 2023 - what year born?

Today, 26 September 2023 if a person is 102 years old now, what year was he born? See below:

If 102 years old, year of birth is:
1920 or 1921*

*It depends on whether he was born before or after 1 January 1921.

If now 102 years and his year of birth 1920 if he was born after 26 September 1920 until 31 december 1920 inclusively, and his year of birth is 1921 if he was born from 1 January 1921 to 26 September 1921.

Other examples:

If now 8 years, year of birth 2014 or 2015
If now 18 years, year of birth 2004 or 2005
If now 19 years, year of birth 2003 or 2004
If now 39 years, year of birth 1983 or 1984

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