123 years old now in 2025 - what year born?

Today, 15 January 2025 if a person is 123 years old now, what year was he born? See below:

If 123 years old, year of birth is:
1901 or 1902*

*It depends on whether he was born before or after 1 January 1902.

If now 123 years and his year of birth 1901 if he was born after 15 January 1901 until 31 december 1901 inclusively, and his year of birth is 1902 if he was born from 1 January 1902 to 15 January 1902.

Other examples:

If now 9 years, year of birth 2015 or 2016
If now 14 years, year of birth 2010 or 2011
If now 19 years, year of birth 2005 or 2006
If now 45 years, year of birth 1979 or 1980

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