All the best!
Riddle

The man's bday was on 31st of December.
Think, the year was 2018.
Therefore; If today is January 1, then day before yesterday would be 30th December.
So,
In 30th December 2018 the man's age was 21,
In 31st December 2018 the man's age would become 22.
Today is 1st January 2019.
In 31st December 2019 the man would become 23.
And in next year's bday, i.e, 2020's bday
The man would be 24
The day before yesterday I was 21, and next year I will be 24. When is my birthday?
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The first one to tell the correct answer will get a cheer.