4 years old now in 2025 - what year born?

Today, 19 December 2025 if a person is 4 years old now, what year was he born? See below:

If 4 years old, year of birth is:
2020 or 2021*

*It depends on whether he was born before or after 1 January 2021.

If now 4 years and his year of birth 2020 if he was born after 19 December 2020 until 31 december 2020 inclusively, and his year of birth is 2021 if he was born from 1 January 2021 to 19 December 2021.

Other examples:

If now 3 years, year of birth 2021 or 2022
If now 12 years, year of birth 2012 or 2013
If now 20 years, year of birth 2004 or 2005
If now 59 years, year of birth 1965 or 1966

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