15 years old now in 2024 - what year born?

Today, 10 October 2024 if a person is 15 years old now, what year was he born? See below:

If 15 years old, year of birth is:
2008 or 2009*

*It depends on whether he was born before or after 1 January 2009.

If now 15 years and his year of birth 2008 if he was born after 10 October 2008 until 31 december 2008 inclusively, and his year of birth is 2009 if he was born from 1 January 2009 to 10 October 2009.

Other examples:

If now 7 years, year of birth 2016 or 2017
If now 18 years, year of birth 2005 or 2006
If now 20 years, year of birth 2003 or 2004
If now 80 years, year of birth 1943 or 1944

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