18 years old now in 2025 - what year born?

Today, 19 December 2025 if a person is 18 years old now, what year was he born? See below:

If 18 years old, year of birth is:
2006 or 2007*

*It depends on whether he was born before or after 1 January 2007.

If now 18 years and his year of birth 2006 if he was born after 19 December 2006 until 31 december 2006 inclusively, and his year of birth is 2007 if he was born from 1 January 2007 to 19 December 2007.

Other examples:

If now 5 years, year of birth 2019 or 2020
If now 12 years, year of birth 2012 or 2013
If now 21 years, year of birth 2003 or 2004
If now 52 years, year of birth 1972 or 1973

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