91 years old now in 2025 - what year born?

Today, 21 May 2025 if a person is 91 years old now, what year was he born? See below:

If 91 years old, year of birth is:
1933 or 1934*

*It depends on whether he was born before or after 1 January 1934.

If now 91 years and his year of birth 1933 if he was born after 21 May 1933 until 31 december 1933 inclusively, and his year of birth is 1934 if he was born from 1 January 1934 to 21 May 1934.

Other examples:

If now 3 years, year of birth 2021 or 2022
If now 15 years, year of birth 2009 or 2010
If now 24 years, year of birth 2000 or 2001
If now 35 years, year of birth 1989 or 1990

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