I still don't know how you stop people of similar ages not getting into a relationship, when they have a common interest? Many long term relationships / marriages start because of people have something in common, be it work, music, food, cinema, multitude of interests, membership/attendance of a group/organisation etc. The unalienable truth is that none of these respect ages or the people.
It is churlish to forbid it. I've never seen anything as to an IA should we be aware of it. Do we kick them out, so what, that's no real loss to them, or, report them to the police and insist on criminal proceedings, can't see that happening, especially if the parents of the "wronged" party say it's OK.
The best thing is for our vastly life experienced sqn cdrs to offer advice and guidance on the matter, rather than running to an internal book/rule and quote chapter and verse, putting the fear of God into them that what they've done is morally and ethically wrong, when it isn't. The single biggest problem is that everyone thinks that the relationships like this are always or going to be physical from day one, when like all relationships they will be largely platonic / just intimate for quite a while.
Don't get me wrong if it was a 25+ taking up with a young lad or lass, that's not right. Just from the POV of who in their right mind (other than celebs and wannabes) would want to be in a relationship with a moody/hormonal teen, when they are much older.