The definition of consent, as far as the law is concerned, is anything but ethereal. It's very clear. Please learn it before you run afoul of the law.
Hint: children, animals and dead people cannot give legal consent.
You're right that the concept of consent as it relates to age HAS changed...it keeps going up thankfully.
Okay, so you start out saying consent is "anything but ethereal" and then go on to explain how it is but that doesn't really matter. There is no set national age of consent that we've all agreed to. An argument can be made that animals and dead people can't give consent therefore it can't be a parameter required. It's no different than saying gay people can marry if they can demonstrate the ability to reproduce. You are placing a demand that can't be met under any circumstance.
And this arbitrary age that we keep moving up... what's up with that? On what basis do we establish someone is suddenly more able to give consent the day after their birthday than the day before? People mature differently, maybe a 13 year old is more mature than an 18 year old... you don't know. Besides, if we remove "morality" (based on religion) from the equation, we see that in nature animals begin to breed when they become sexually mature. Why can't this be made the case with humans? ...Other than some morally-based idea and preconception that is frankly antiquated in this modern day and time?
It seems that suddenly, you perverts want to get all tight-assed and proselytize about your morals when it comes to "consent" and age of consent, or in applying consent where the parameter can't possibly be met. Do you really think future generations are going to give a shit about your moral hang ups? Haven't you made your case on this being more about rights than morals of society? It seems to be fine and dandy as long as you're going after what you want but you turn into a complete hypocrite when it comes to something you're uncomfortable with. Then, you want to break out the bibles and hymnals and talk about protecting our children from the evils of the world.... as if that has any damn thing to do with their rights as humans to give their own consent.
Twenty years ago, you couldn't legally consent to homosexual acts. So we see, legal consent can obviously be changed and it has been. In fact, it is far easier to change than the definition of a 3,000 year old tradition rooted in religious belief. And speaking of religious beliefs, what about Muslims who religiously believe in child marriage? Who are YOU to question their morals?