That is a fact. But they can screw each other, if they’re old enough. But they’r still classified as kids. “Adolescent kid” is a subjective term, and I would even suggest raising the age higher than 16: until they’re legally adults.
I think the question is coming from a “why is it different in different countries” point of view.
I’m not going to Google it and put myself on a watch list, but I think I recall hearing some back-asswards country where the age of “consent” was 14, or some even lower. Culturally that doesn’t make any sense to me - but then i agree with you that kids shouldn’t be screwer nor screwee.
The other ages are interesting too - in the UK we wait for our teens to grow up a bit before putting them behind the wheel of a car. The driving age is 18 - and forget even getting affordable insurance until you’re 25 anyway.