123 years old now in 2024 - what year born?

Today, 10 October 2024 if a person is 123 years old now, what year was he born? See below:

If 123 years old, year of birth is:
1900 or 1901*

*It depends on whether he was born before or after 1 January 1901.

If now 123 years and his year of birth 1900 if he was born after 10 October 1900 until 31 december 1900 inclusively, and his year of birth is 1901 if he was born from 1 January 1901 to 10 October 1901.

Other examples:

If now 5 years, year of birth 2018 or 2019
If now 16 years, year of birth 2007 or 2008
If now 18 years, year of birth 2005 or 2006
If now 68 years, year of birth 1955 or 1956

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