121 years old now in 2025 - what year born?

Today, 19 December 2025 if a person is 121 years old now, what year was he born? See below:

If 121 years old, year of birth is:
1903 or 1904*

*It depends on whether he was born before or after 1 January 1904.

If now 121 years and his year of birth 1903 if he was born after 19 December 1903 until 31 december 1903 inclusively, and his year of birth is 1904 if he was born from 1 January 1904 to 19 December 1904.

Other examples:

If now 11 years, year of birth 2013 or 2014
If now 17 years, year of birth 2007 or 2008
If now 28 years, year of birth 1996 or 1997
If now 73 years, year of birth 1951 or 1952

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