123 years old now in 2023 - what year born?

Today, 1 December 2023 if a person is 123 years old now, what year was he born? See below:

If 123 years old, year of birth is:
1899 or 1900*

*It depends on whether he was born before or after 1 January 1900.

If now 123 years and his year of birth 1899 if he was born after 1 December 1899 until 31 december 1899 inclusively, and his year of birth is 1900 if he was born from 1 January 1900 to 1 December 1900.

Other examples:

If now 5 years, year of birth 2017 or 2018
If now 18 years, year of birth 2004 or 2005
If now 27 years, year of birth 1995 or 1996
If now 42 years, year of birth 1980 or 1981

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