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?