It is reasonable to assume she was 16. This is why he wasn't sentenced.
Yes.
Under the law It is rape everyone, she can verbally and physically consent as much she wants but legally she can't because she is too young so whoever she chooses to have sex with is under the law raping her.
As I said, I don't know anything about Scottish (or English law.).
However, where I studied law (civil law country, btw) intent is necessary for the act of rape.
So, the perpetrator needs to have the knowledge of the facts that make his actions rape or it is deemed that he should have known these facts/that an objective 3rd person in his shoes would have known.
But as I said before, she looked above the age of consent, acted like she was, probably had a fake ID, said she was and appared to have given consent.
I fail to see how the alleged perpetrator (imo actually also a victim!!) could have known any of that. Or can be expected to have somehow known any of this when other people apparently also thought she was much older than 12!