Just be like "hey chill u r being boy crazy" or what you should do (and this really works) make jokes about it-in a nice way. Like randomly when you are just joking around and goofing off bring it up as a joke...in a way that shows u aren't joking at all bit bot in a bad way.
Before you say something to someone maybe you should think is it kind? Is it true? Is it nessaccary? Does it improve upon the silence? If its no to anyone of these don't say it. Being boy crazy is pretty normal at a young age.