25 years old now in 2023 - what year born?

Today, 1 December 2023 if a person is 25 years old now, what year was he born? See below:

If 25 years old, year of birth is:
1997 or 1998*

*It depends on whether he was born before or after 1 January 1998.

If now 25 years and his year of birth 1997 if he was born after 1 December 1997 until 31 december 1997 inclusively, and his year of birth is 1998 if he was born from 1 January 1998 to 1 December 1998.

Other examples:

If now 6 years, year of birth 2016 or 2017
If now 15 years, year of birth 2007 or 2008
If now 25 years, year of birth 1997 or 1998
If now 91 years, year of birth 1931 or 1932

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