The minor can annul the contract at any time, simply because he/she is a minor. However, once the minor hits the legal age, the contract must be reaffirmed. Alternately, if the contract continues for a certain period (6 months???), it is reaffirmed by the absence of a cancellation.
For this reason, in American law, it is bad business to sign contracts with minors. The minor can hold the other party responsible to the contract. But, the minor can annul it at any time.
I am recalling this from a class taken about 6 months ago.
However, the law that will govern, be it international law, Indian law, or English law, depends on the terms of the contract. It is lawful for a contract to specify the governing law- a very important part of international contracts.
A properly drawn contract will specify which law governs.
In English law, the government has the power and the authority to protect the property of minors. This principal is called "parens patriae". A minor is considered a person "non sui juris".
India has a similar claim to represent the people. You might find something interesting in Charan Lal Sahu v. Union of India (1984 Union Carbide lawsuits)