21 years old now in 2024 - what year born?

Today, 14 October 2024 if a person is 21 years old now, what year was he born? See below:

If 21 years old, year of birth is:
2002 or 2003*

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

If now 21 years and his year of birth 2002 if he was born after 14 October 2002 until 31 december 2002 inclusively, and his year of birth is 2003 if he was born from 1 January 2003 to 14 October 2003.

Other examples:

If now 12 years, year of birth 2011 or 2012
If now 17 years, year of birth 2006 or 2007
If now 25 years, year of birth 1998 or 1999
If now 33 years, year of birth 1990 or 1991

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