90 years old now in 2025 - what year born?

Today, 23 January 2025 if a person is 90 years old now, what year was he born? See below:

If 90 years old, year of birth is:
1934 or 1935*

*It depends on whether he was born before or after 1 January 1935.

If now 90 years and his year of birth 1934 if he was born after 23 January 1934 until 31 december 1934 inclusively, and his year of birth is 1935 if he was born from 1 January 1935 to 23 January 1935.

Other examples:

If now 9 years, year of birth 2015 or 2016
If now 13 years, year of birth 2011 or 2012
If now 21 years, year of birth 2003 or 2004
If now 71 years, year of birth 1953 or 1954

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