My 21 year old son had consensual sex with a 15 year old girl.

Hello:

If your son made all reasonable efforts to determine her age and was still under the assumption that she was over 16, he can have a defence.

Usually the sexual activity of the victim is not admissible in evidence. This is to prevent a situation where the accused tries to portray the victim as someone less worthy of protection of the law because of promiscuity, or less likely of belief because of her past choices.

It is possible to admit such evidence, but an application must be made first to the trial judge, showing why such evidence is necessary for the defence. There would need to be some proof that your son was aware of the prior sexual history, and that this played into his belief that this girl was maybe older than 15. If the judge is not convinced that this evidence is reliable, then the judge must refuse admission of the evidence.

So evidence of her sexual history it can be admitted if this exception is met, but otherwise details as to who or when this person consented to sex has no bearing. She does not gain the legal ability to consent to sex with your son just because she had consensual sex with others where she may also have been legally incapable of giving such consent.