There was no sin committed. Part of growing up, boys deal with that aspect in their life. It isn’t asked for and not wanted. It is embarrassing to them. They don’t understand what is happening.
As for ScrupulousMonk to say that it is a intrinsic sin is not correct from what I know.

You don’t control what you dream nor what happens in your dream. Personally I think that for some reason ScrupulousMonk thinks you had this dream he is saying that you somehow sinned. I would look more into to that.
I’m not sure what classica87 means by asking if it was a sin, you have just failed one of the requirements of a mortal sin. What does it mean by asking if something is a sin that one has just failed the requirements of a mortal sin? Does it mean that it isn’t a mortal sin or because asking about it becomes a mortal sin?
I was in an RCIA class and a gentlemen ask the priest about if it was a sin when sudden unwanted thoughts came into him mind. The priest told him that we can’t control all the thoughts that come to our minds especially the unwanted thoughts. We can try. Which I find helpful because of the fact I deal with mental illness and have thoughts that as hard as try won’t leave me alone. I do spend time talking with my priest about this and it helps to have a good priest to talk when you are not sure about things.
My suggestion to you TheHolyTrinity9 is to talk to your priest about this instead on topics like this because he will knows you and will how to deal with how you are feeling.
IMHO,
kehanson