A male of the age of less than 21 years and a female of the age of less than 18 years are considered as “child” under the provisions of the Prohibition of Child Marriage Act, 2006, which is equally applicable to Hindus.
A marriage in which either of the parties is a child is considered as a child marriage.
Section 3 of the above Act lays down that every child marriage, whether solemnised before or after the commencement of this Act, shall be voidable at the option of the contracting party who was a child at the time of the marriage.
Therefore, as asked in your question, the marriage of a boy of the age of 20 years and girl of the age of 17 years will be voidable.
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