Age is totally irrelevant as to how the institution of marriage works. A man with 30 wives would be 30 individual marriages.

The traditional institution of marriage automatically acknowledges diversity, i.e., male and female in physical reality, which automatically acknowledges and differentiates the true dichotomy of male and female human relations in physical reality, mating from mating less in physical reality, and especially acknowledges that a man and a woman who mate with each other and don't produce a baby are not mating less human relations in physical reality. Allowing two people of the same sex to also be married literally changes what's being acknowledged in physical reality, i.e., two people of the same sex cannot be acknowledged as mating in physical reality because a man and a woman can be acknowledged as mating less in physical reality, which is the one and only way to redefine the traditional institution of marriage and the one and only way to do so. Everything else is purely optional. Mating and mating less are the only human relations that actually exist in physical reality for the institution of marriage to acknowledge and differentiate between which is why this is how the institution of marriage works, regardless of accuracy of any particular marriage. The way to acknowledge a man and a woman as simply mating less with the traditional institution of marriage is to acknowledge that they're not married to each other. Acknowledging that two people are not married with each other with the redefined institution of marriage will also acknowledge that they're simply mating less. Rape, incest, prostitution, unlawful carnal knowledge, adultery, homosexuality, are all predicated on actions in physical reality, mating and mating less. An act of rape, an act of incest, etc, and are differentiated by what the actions are being acknowledged as, rape from all other human relations that are not rape, whatever rape may be. The institution of marriage acknowledges and differentiates status in physical reality, mating from mating less or mating less from mating, they're married or that man and woman are married to each other. Human beings are not biologically designed to produce a baby every time a man and a woman mate, i.e., actions in physical reality. Human beings are biologically designed to perpetuate the human species with heterosexual reproduction, i.e., status in physical reality. Mating and mating less also apply to individual human beings, virgin and heterosexual. Genetics and brain structure are totally irrelevant. Homosexual is pure make believe. It doesn't exist in physical reality. It never has and it never will. A group marriage of three or more people acknowledges a group of people in physical reality, like a flock of birds or a herd of cattle there would be a group marriage of humans. If two people of the same sex are only allowed to be married that would also be group marriage. To honor, to have and to hold, to love and to cherish are reasons for getting married and is purely optional. Which is why two peopl can vow to love each other and vow to hate each other at the same time, regardless of accuracy of any particular marriage.