51 years old now in 2023 - what year born?

Today, 10 June 2023 if a person is 51 years old now, what year was he born? See below:

If 51 years old, year of birth is:
1971 or 1972*

*It depends on whether he was born before or after 1 January 1972.

If now 51 years and his year of birth 1971 if he was born after 10 June 1971 until 31 december 1971 inclusively, and his year of birth is 1972 if he was born from 1 January 1972 to 10 June 1972.

Other examples:

If now 12 years, year of birth 2010 or 2011
If now 15 years, year of birth 2007 or 2008
If now 25 years, year of birth 1997 or 1998
If now 76 years, year of birth 1946 or 1947

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