The age of consent seems to arise because people under a certain age threshold are not capable of making informed, prudent decisions. Because of Neurology or Wisdom or otherwise. However what is to say that they are capable when past this age threshold? Consider an alien species similar to us however they live to the age of 1000 rather than 80-100 as in humans. This alien species might give the age of consent to 200 years because anyone younger is deemed not having enough knowledge to make an informed decision. When this alien species looks at us they will probably pity us for making choices below the age of 200, because we have not the wisdom nor the neurology that is required to make an informed decision. Is the age one has to make an informed decision thus meaningless?

My suspicion is that you may be holding "informed decision" to an unfairly high standard. Granted, we often do not make "informed, prudent decisions." We human beings are certainly not omniscient, and we sometimes reason badly. But plenty of decisions we make can be made rationally without being omniscient: I don't have to know all that much to (say) choose between a salad and an omelette for lunch, or to decide whether to have a summer or a winter vacation this year. Of course, some decisions are more complicated. But I'm happy to say that we have enough knowledge in many cases to make decisions that meet minimal standards of rationality. You may also be making the controversial assumption that the only factor relevant to "age of consent" is rationality. Ethically speaking, certain decisions matter a lot to us because they impinge on fundamental concerns. Whom to marry, for example, is not a decision that others should make for us. For one, even if I'm not perfectly rational about that decision, I'm...