You're right of course, the young people (I'm off course talking in generality of the modal opinion) could be misguided in what they wanted, but they wanted it.
I suppose it's also possible there was a cadre of older people who felt the young would be better out of the EU - the same problems but no say in how to fix them and less cooperation, that's got to help /s - but who choose to keep silent about that position?
You're making assumptions there as to peoples' individual motivations. Just because someone voted in a way that you deem is not in the best interests of another group doesn't mean that they didn't have that group's best interest in mind.
I personally think this is a good thing for both young and old people. So in your mind, me voting to "leave" would actually be me not-voting in the interests of the young?