5 years old now in 2023 - what year born?

Today, 30 November 2023 if a person is 5 years old now, what year was he born? See below:

If 5 years old, year of birth is:
2017 or 2018*

*It depends on whether he was born before or after 1 January 2018.

If now 5 years and his year of birth 2017 if he was born after 30 November 2017 until 31 december 2017 inclusively, and his year of birth is 2018 if he was born from 1 January 2018 to 30 November 2018.

Other examples:

If now 3 years, year of birth 2019 or 2020
If now 15 years, year of birth 2007 or 2008
If now 24 years, year of birth 1998 or 1999
If now 51 years, year of birth 1971 or 1972

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