A marriage is void from the time its nullity is declared by a court of competent jurisdiction if either party thereto:

1. 1. Is under the age of legal consent, which is eighteen years;
2. 2. Is incapable of consenting to a marriage for want of understanding;
3. 3. Is incapable of entering into the married state from physical cause;
4. 4. Consent to such marriage by reason of force, duress or fraud;
5. 5. Has been incurably mentally ill for a period of five years or more.