I'll do my best to state a positive theory rather than dismissing this as hemlines. Then you'll all call me names, and then we can drop it.
1. Women are perpetually under threat of violence from men. This is what Dworkin meant by "vaginal penetration as an invasive dynamic under patriarchy." This is why rape of women by men is bad, and why we should have laws against it, and why we can use age as a stand-in for consent for Mf (older male, younger female).
2. The age you use to ban Mf is socially negotiated. The historical standard was a period is God's green light. I was raised in our society, so I think that's too young for the female, but if your whole society sets it as 13 or 17 or 21 or 25, have at it. Who am I to judge?
3. mF is entirely different. Males are obsessed with sex. Females are circumspect. They have to be; the risks fall on them. Applying the same age to both Mf and mF is merely the laziness of the state. The question then becomes, given the society we all share -- and I assure you as an aside I personally share your brain worms -- how do we arrive at a mF age?
4. The current paradigm is cognitive maturity, however we even violate that standard. Male brain development lags behind female. At lowest, the male child-to-adult cutoff, if we were serious, would be around 21, though I've read 22 or 23 is probably a better standard. As such, if we honored our own standard, a 19-year old male having sex with a 27-year old female ought to be prosecuted as rape. It is not. Therefore, all the rage is hypocrisy. Something else is going on behind the current law and the socially-enforced (witness this thread) anger.
5. My positive theory: cognitive capacity is our version of what in prior ages was fully believed to be the duty to protect sacred virignity. It is this century's demand that a law of the head supercedes the law of the body. This goes back to The City of God and well before. It goes back to the perennial Puritanical screech that the body is sinful and bad and the mind is pure and good.
I reject this propaganda the mind puts out there to demand authoritarian control of the Self. The mind grows out of and is part of the body, and any attempt to call it entirely separate by Plato, Augustine or Descartes is driven by anxiety and fear of our substrate. The mind wants certain things; the body wants certain things. Often they agree; often they are in conflict. Because humans are both obsessed with and repelled by their sexuality, we spend a lot of our time making up reasons to deny ourselves pleasure. Catholics and Calvinists are infamous, but we all do it. Our current justification -- more than that, honest belief -- in the mF cutoff is another such instance. It is highly suspect.
Now, I personally subscribe to it, just like you. But I don't believe everything I believe should go for everyone else. I am not the end of history, nor is my society.
This concludes my lecture. "A poor argument requires many words" and all that, but you know me, why use 10 words when 1000 will do? If you want to burn me in effigy, at least do me the courtesy of reading it with an open mind before gathering the straw.