115 years old now in 2025 - what year born?

Today, 21 May 2025 if a person is 115 years old now, what year was he born? See below:

If 115 years old, year of birth is:
1909 or 1910*

*It depends on whether he was born before or after 1 January 1910.

If now 115 years and his year of birth 1909 if he was born after 21 May 1909 until 31 december 1909 inclusively, and his year of birth is 1910 if he was born from 1 January 1910 to 21 May 1910.

Other examples:

If now 5 years, year of birth 2019 or 2020
If now 14 years, year of birth 2010 or 2011
If now 20 years, year of birth 2004 or 2005
If now 33 years, year of birth 1991 or 1992

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