The states are limited by the U. S. Constitution. “Marriage” isn’t in there but life, liberty, and property is.
Marriage is a old established common law contract, and as a contract is a form of property right.
What prevents a state Justice Tanney from redefining anyone younger than 30 days and older than 90 years as no longer alive?
There are absolutes. Proverbs puts it thus "Remove not the old landmark; and enter not into the fields of the fatherless".
The old landmarks include the basic -- self-evident to the Founder's generations -- definitions of marriage, of murder, of life, of WHO IS A MAN. Justice Tanney busted down that last old landmark, and as a consequence a most bloody civil war ensued.
A state can place some constraints on what constitutes a legally recognizable marriage, or define categories of murder. But there are some limits to the ability to redefine basic concepts and terms of law.
The modern folly of redefining marriage is as bad or worse than what Justice Tanney once did.