so many people have constructed magical beliefs about turning 18. everyone loves the idea that 18 years old is exactly when everyone becomes an adult because it gives you easy answers to a bunch of thorny questions about statutory rape and grooming but it simply does not line up with reality. there is no special significance to "being alive for 18 years" that makes people adults who are able to have healthy balanced relationships with other adults. there is not a discrete cutoff after which a person is "ready" to date adults, or have sex, or anything else. it's all contextual, it's all individual, it's all culturally defined. instead of trying to simplify your ethics down to mathematical equations and numerical constants, consider using your brain!
the idea that if you show a 17 year old your boobs it's an Evil Unforgivable Sex Crime but if you show an 18 year old your boobs it's just normal intimacy between adults is patently absurd on its face, and yet a huge amount of people take it as an unassailable fact when constructing ontologies of "good" and "bad" sex acts!
