20 years old now in 2023 - what year born?

Today, 22 March 2023 if a person is 20 years old now, what year was he born? See below:

If 20 years old, year of birth is:
2002 or 2003*

*It depends on whether he was born before or after 1 January 2003.

If now 20 years and his year of birth 2002 if he was born after 22 March 2002 until 31 december 2002 inclusively, and his year of birth is 2003 if he was born from 1 January 2003 to 22 March 2003.

Other examples:

If now 10 years, year of birth 2012 or 2013
If now 13 years, year of birth 2009 or 2010
If now 18 years, year of birth 2004 or 2005
If now 81 years, year of birth 1941 or 1942

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