Section 2 of the Hindu Marriage Act, 1955 says:

This Act applies :

1. to any person who is a Hindu by religion in any of its forms or developments,
2. to any person who is a Buddhist, Jain or Sikh by religion; and
3. to any other person domiciled in the territories to which this Act extends who is not a Muslim, Christian, Parsi or Jew by religion, unless it is proved that any such person would not have been governed by the Hindu law or by any custom or usage as part of that law in respect of any of the matters dealt with herein if this Act had not been passed.

This section therefore applies to Hindus by religion in any of its forms and Hindus within the extended meaning i.e. Buddhist, Jains or Sikh and, in fact, applies to all such persons domiciled in the country who are not Muslims, Christians, Parsi or Jew, unless it is proved that such persons are not governed by the Act under any custom or usage. The Act applies to Hindus outside the territory of India only if such a Hindu is domiciled in the territory of India

Section 5 of Hindu Marriage Act, 1995

A marriage may be solemnized between any two Hindus, if the following conditions are fulfilled, namely

1. Neither party has a spouse living at the time of the marriage
2. At the time of the marriage, neither party-

• is incapable of giving a valid consent to it in consequence of unsoundness of mind; or
• though capable of giving a valid consent, has been suffering from mental disorder of such a kind or to such an extent as to be unfit for marriage and the procreation of children;

3. The bridegroom has completed the age of twenty-one years and the bride the age of eighteen years at the time of the marriage;
4. The parties are not within the degrees of prohibited relationship unless the custom or usage governing each of them permits of a marriage between the two;