I'm too much of a nihilist to discuss "morality", but I get where are you commin from. We all have our own point of view, all is good.
Well, I am a moral nihilist in the sense that I don't think there is such a thing as an objective morality. Well, objective morality is established when there are enough subjective minds to agree that an objective morality needs to be in place (e.g., murder is against the law).
Anyway, as I said, 18 is the legal age in America, so if some guy wants to sleep with an 18 year old, that's his business. Anything below 18, which may break the law, I have an issue with.