I don't think the Texas homosexual sodomy issue was a matter of legal consent, but instead a matter of an overall illegal act. That to me is different from sex with a minor -- because a minor can't enter into contracts or legally consent to anything (nore can an animal, by the way). In the first case, it was consensual, but not legal. In the latter, it is illegal and also by definition non-consensual.
The age of consent is arbitrary as proven by the differences in state laws and national laws.