12 years old now in 2023 - what year born?

Today, 30 November 2023 if a person is 12 years old now, what year was he born? See below:

If 12 years old, year of birth is:
2010 or 2011*

*It depends on whether he was born before or after 1 January 2011.

If now 12 years and his year of birth 2010 if he was born after 30 November 2010 until 31 december 2010 inclusively, and his year of birth is 2011 if he was born from 1 January 2011 to 30 November 2011.

Other examples:

If now 5 years, year of birth 2017 or 2018
If now 18 years, year of birth 2004 or 2005
If now 30 years, year of birth 1992 or 1993
If now 44 years, year of birth 1978 or 1979

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