90 years old now in 2023 - what year born?

Today, 24 September 2023 if a person is 90 years old now, what year was he born? See below:

If 90 years old, year of birth is:
1932 or 1933*

*It depends on whether he was born before or after 1 January 1933.

If now 90 years and his year of birth 1932 if he was born after 24 September 1932 until 31 december 1932 inclusively, and his year of birth is 1933 if he was born from 1 January 1933 to 24 September 1933.

Other examples:

If now 7 years, year of birth 2015 or 2016
If now 18 years, year of birth 2004 or 2005
If now 25 years, year of birth 1997 or 1998
If now 85 years, year of birth 1937 or 1938

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