The key to understanding the Act is this: the law says 16 is the dividing line.
If a person is 16 or above they can give consent to sexual activity which can be accepted by their partner.
If they are 15 or below (child) they cannot.
If a child is between the age of 13 and 16 and agrees to the sexual activity, and the person of 18 or over (adult) reasonably believed that the child was 16 or over, no offence is committed.
In other words, the adult can lawfully accept the child’s consent if they reasonably believe they are not a child.
Whether or not the child consented to the activity, if they are 12 years old or below, then the reasonableness or otherwise of the adult’s belief about their age is irrelevant.
Therefore for an adult to engage in sexual activity with a child of 12 years or below is always a crime.
What if a 17-year-old boy engages in sexual activity with his 14-year-old girlfriend?
The boy is of an age whereby when he can lawfully consent to sexual activity but his 14-year-old girlfriend, being 15 or under, is too young.
If the boy knows she is 14 he commits an offence.
If he reasonably believes her to be 16 or over, and that belief is objectively reasonably held (a matter for a Jury) then he has defence.
What if a 15-year-old boy engages in sexual activity with his 13-year-old girlfriend?
The boy is guilty of a crime if he knows that his girlfriend is only 13.
The girl is equally guilty of a crime if she knows her boyfriend is 15.
What if a 15-year-old boy is having sexual intercourse with his 12-year-old girlfriend?
This is rape. As stated above, the 12-year-old girl cannot consent to the activity.
For those in positions of trust over children, such as teachers, the “age of consent” of 16 moves up to 18.
Therefore if a female teacher of 30 engages in sexual activity with a boy of 17 who is one of her pupils, she commits an offence unless she reasonably and objectively believes that he is 18 or over.