12 years old now in 2024 - what year born?

Today, 12 September 2024 if a person is 12 years old now, what year was he born? See below:

If 12 years old, year of birth is:
2011 or 2012*

*It depends on whether he was born before or after 1 January 2012.

If now 12 years and his year of birth 2011 if he was born after 12 September 2011 until 31 december 2011 inclusively, and his year of birth is 2012 if he was born from 1 January 2012 to 12 September 2012.

Other examples:

If now 9 years, year of birth 2014 or 2015
If now 13 years, year of birth 2010 or 2011
If now 24 years, year of birth 1999 or 2000
If now 50 years, year of birth 1973 or 1974

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