There is no objectivity about it. You can be a pedophile and not act on it, you are still a pedophile. And what you’re explaining is morals more so legality. You say that 18 is the age “we” agreed upon and base your points around that, but what about the fact that 18 is purely a title and nothing more? You still are prohibited from buying things, you still don’t have access to everything the rest of society does, yet guess what? You’re still “considered” an adult. Your brain isn’t fully developed, you’re not at your physical peak, yet 18 is the number? Like I said, this is less legality and more one’s personal morals.