20 years old now in 2025 - what year born?

Today, 23 January 2025 if a person is 20 years old now, what year was he born? See below:

If 20 years old, year of birth is:
2004 or 2005*

*It depends on whether he was born before or after 1 January 2005.

If now 20 years and his year of birth 2004 if he was born after 23 January 2004 until 31 december 2004 inclusively, and his year of birth is 2005 if he was born from 1 January 2005 to 23 January 2005.

Other examples:

If now 8 years, year of birth 2016 or 2017
If now 16 years, year of birth 2008 or 2009
If now 25 years, year of birth 1999 or 2000
If now 95 years, year of birth 1929 or 1930

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