18 years old now in 2024 - what year born?

Today, 10 October 2024 if a person is 18 years old now, what year was he born? See below:

If 18 years old, year of birth is:
2005 or 2006*

*It depends on whether he was born before or after 1 January 2006.

If now 18 years and his year of birth 2005 if he was born after 10 October 2005 until 31 december 2005 inclusively, and his year of birth is 2006 if he was born from 1 January 2006 to 10 October 2006.

Other examples:

If now 4 years, year of birth 2019 or 2020
If now 13 years, year of birth 2010 or 2011
If now 18 years, year of birth 2005 or 2006
If now 93 years, year of birth 1930 or 1931

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