121 years old now in 2023 - what year born?

Today, 29 May 2023 if a person is 121 years old now, what year was he born? See below:

If 121 years old, year of birth is:
1901 or 1902*

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

If now 121 years and his year of birth 1901 if he was born after 29 May 1901 until 31 december 1901 inclusively, and his year of birth is 1902 if he was born from 1 January 1902 to 29 May 1902.

Other examples:

If now 4 years, year of birth 2018 or 2019
If now 15 years, year of birth 2007 or 2008
If now 21 years, year of birth 2001 or 2002
If now 97 years, year of birth 1925 or 1926

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