(a) In a judicial, administrative, or other proceeding, the marriage of a man and woman may be proved by evidence that:

(1) a declaration of their marriage has been signed as provided by this subchapter; or

(2) the man and woman agreed to be married and after the agreement they lived together in this state as husband and wife and there represented to others that they were married.

(b) If a proceeding in which a marriage is to be proved as provided by Subsection (a)(2) is not commenced before the second anniversary of the date on which the parties separated and ceased living together, it is rebuttably presumed that the parties did not enter into an agreement to be married.

(c) A person under 18 years of age may not:

(1) be a party to an informal marriage; or

(2) execute a declaration of informal marriage under Section 2.402.

(d) A person may not be a party to an informal marriage or execute a declaration of an informal marriage if the person is presently married to a person who is not the other party to the informal marriage or declaration of an informal marriage, as applicable.