This is the first clause of the 14th amendment (emphasis added):

All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside. No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws.

The plain text meaning of that requires legal equality between women and men.

True, it has not been interpreted in that fashion. And because of that, I support the ERA. But until the ERA is ratified, I suggest no one has to look far or work hard to find a provision of our own Constitution requiring legal equality among citizens, and defining women as equal citizens.

You write:

In fact, it has been interpreted in that fashion to a great degree. For example, in Craig v. Boren, 429 U.S. 190 (1976), the Supreme Court invalidated an Oklahoma law that provided different minimum ages for males and females to buy beer. In United States v. Virginia, 518 U.S. 515 (1996), the Court held that the Equal Protection Clause was violated by Virginia Military Institute's males-only admission policy. (The Court was not deterred by the State's offer to set up a "separate but equal" facility for women.) VMI was the last U.S. military college to admit women, but finally did so after losing in the Supreme Court, and is coeducational to this day.

Justice Ginsburg wrote the majority opinion in the VMI case. By that decision, she somewhat undercut her own criticism of the Constitution.