... is there a certain point where you can step on any beat you want or dance the melody line? Not talking about choreography or routines.
Of course, to point out the obvious,
there's improvisation (unabashed gesticulation, in all its misinformed, uneducated, and ill-suited glory),
and there's improvisation (see post 99 : http://dance-forums.com/showpost.php?p=821393&postcount=99)
I heard that Foxtrot used to be that way a loooong time ago, but I was wondering if it's still taught that way in ballroom social dancing today.
One of the bad bad boys in all that is the underlying business method in teaching it---perpetuated by the zealous acolytes of the stodgily pedantic (but that's a different thread---viva la revolucion!).
But I digress.
The irony of it all (and I guess my point and answer to your question) is, in the hands of the right TECHNICAL teacher, you can learn improvisation early--in this instance, ballroom, but certainly true for ANY dance (true, at least in my experience with my mentors).
IMO, the more TECHNICALLY ADEPT the teacher is, the better the understanding of how to improvise---which can only translate to their students' picking-up the ability.