I do have to say that I agree with Katka on this. When mentally challenged (notice I didn't say retards) people are involved, then there is no such thing as consensual. These people do not have the mental capacity to make choices on their own, that is why they were in a center for mentally disabled youth in the first place.
There is no way of telling, but I can almost guaruntee you that the 14 year old was "influenced" by the 18 year old. I have noticed that with people who are not as mentally sharp, that it is all in how you phrase the question. If you ask a senior citizen who isn't all with it anymore, "Do you want a cookie?", like it is a good thing, then they will probably say yes. But, if you ask "You don't want a cookie do you?", like it is something bad, they will commonly say no.
But on the other hand, the 18 year old not only shouldn't be in jail at all... period. He should be in a special center for mentally disabled people, cared for under close watch, and not given the oppurtunity to do this again. He should not recieve all of the freedoms of a regular citizen (by "law" he is a criminal after all), but he should under no circumstances be put in a regular prison.
The 14 year old might not have known what he was doing, but did you guys ever think of the fact that the 18 year old might not have know what he was doing either?