4 years old now in 2025 - what year born?

Today, 19 April 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 April 2020 until 31 december 2020 inclusively, and his year of birth is 2021 if he was born from 1 January 2021 to 19 April 2021.

Other examples:

If now 7 years, year of birth 2017 or 2018
If now 17 years, year of birth 2007 or 2008
If now 30 years, year of birth 1994 or 1995
If now 49 years, year of birth 1975 or 1976

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