1. The fact that a female is "sexually mature," by which I assume you mean "menstruating," which nowadays (with all the hormones in the food) starts as early as eight years old does not necessarily mean that she is mature enough to have sex. This is because females are more than just functional receptacles for sperm.
2. No means no. Proceeding on the basis of any other assumption is a really bad idea.
3. At what age a child is capable of "consent" is a very difficult question. Children have an absolute need for love and will trade almost anything for it. They will allows themselves to be sexually used, beaten, starved, punished, "educated," you-name-it, just so long as they are "loved." This places a great responsibility on the adults -- because children and adolescents will allow themselves to be raped in exchange for a little affection. "Abuse" is not the same as having sex. But in my whole entire life I have only heard one story of a child having sex with an adult that was not a story of abuse. (I heard it from the now-grown child)
4. Having sex with old creepy men you don't like has long been one price of admission to Hollywood; or as Marilyn told Louella when she decided to marry Di Maggio "Honey, I've just sucked my last cock." But that doesn't make it right.
5. On the other hand, the demonization of sexual abuse really bothers me when I think of the vast amount of other forms of abuse (which are perfectly acceptable and legal) that children are exposed to.
6. The sexual abuse of children and adolescents by parents, family members, and friends of family is extremely common. I don't think of it as a perversion. I think of it as another heart-rending example of our lack of compassion and love. It just happens to involve sex.
Joanna