A marriage is void from the time its nullity is declared by a court of competent jurisdiction if either party thereto:
1. Is under the age of legal consent, which is eighteen years, provided that such nonage shall not of itself constitute an absolute right to the annulment of such marriage, but such annulment shall be in the discretion of the court which shall take into consideration all the facts and circumstances surrounding such marriage;
2. Is incapable of consenting to a marriage for want of understanding;
3. Is incapable of entering into the married state from physical cause;
4. Consent to such marriage by reason of force, duress or fraud;
5. Has been incurably mentally ill for a period of five years or more.