104 years old now in 2025 - what year born?

Today, 18 January 2025 if a person is 104 years old now, what year was he born? See below:

If 104 years old, year of birth is:
1920 or 1921*

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

If now 104 years and his year of birth 1920 if he was born after 18 January 1920 until 31 december 1920 inclusively, and his year of birth is 1921 if he was born from 1 January 1921 to 18 January 1921.

Other examples:

If now 5 years, year of birth 2019 or 2020
If now 14 years, year of birth 2010 or 2011
If now 28 years, year of birth 1996 or 1997
If now 83 years, year of birth 1941 or 1942

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