Why do young boys crossdress? Because they haven't yet learned they're not supposed to. So they follow their natural instinct.
Why does it "develop into a fetish" during their teens. Because they've learnt they aren't supposed to crossdress and are perfecting their false presentation. However the amazing power of sexual energy in puberty drives them past the self-imposed blockade. They begin to believe their natural instinct is in fact a sexual deviation when it's really natural behavior that can only get past the filter with the aid of sexual energy.
Why does it eventually come back to feelings? Because the sexual energy damps down but the desire to follow their natural path remains and they start to listen.
Does that square up with your theory?
