That is true but this also applies:
"However, if the person is under the other party's guidance or a similar relationship prevails, the higher limit of 18 years applies."
Nevertheless, these rules of "legal archeology" are horrible. Normal standards of evidence do not apply.
In some USA states, specifically Florida, it is not against the law for 16-17 year old kids to have consensual sex if their partner is under 24 years of age.