48 years old now in 2023 - what year born?

Today, 23 September 2023 if a person is 48 years old now, what year was he born? See below:

If 48 years old, year of birth is:
1974 or 1975*

*It depends on whether he was born before or after 1 January 1975.

If now 48 years and his year of birth 1974 if he was born after 23 September 1974 until 31 december 1974 inclusively, and his year of birth is 1975 if he was born from 1 January 1975 to 23 September 1975.

Other examples:

If now 5 years, year of birth 2017 or 2018
If now 12 years, year of birth 2010 or 2011
If now 22 years, year of birth 2000 or 2001
If now 64 years, year of birth 1958 or 1959

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