It is always illegal to carry out sexual acts towards children under 15
According to the law, a child under 15 years of age can never give consent to participate in a sexual act. It doesn’t matter who the other person is or if the child says or shows that they want to have sex.
One exception is when people who are almost the same age have consensual sex, for example if they are in a relationship as a couple. If it is obvious that they both want to have sex with each other voluntarily, the person over 15 should not be convicted of a criminal offence.
A person who has carried out sexual acts towards a child under 15 can be convicted of a crime even if they believed that the child was older. If so, the perpetrator was negligent for failing to find out the person’s age.