20 years old now in 2025 - what year born?

Today, 24 April 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 24 April 2004 until 31 december 2004 inclusively, and his year of birth is 2005 if he was born from 1 January 2005 to 24 April 2005.

Other examples:

If now 5 years, year of birth 2019 or 2020
If now 12 years, year of birth 2012 or 2013
If now 28 years, year of birth 1996 or 1997
If now 71 years, year of birth 1953 or 1954

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