Basically, I'm having trouble which level I should trade my Onix. I was thinking to trade her at level 19 so she can learn Steelix's moves. But, is it too early to do that in the game?
Just evolve it as early as possible because the only move that onix learns that steelix does not is sand tomb which is pretty much useless but if you really want that move, wait until level 46 because thats when it learns it. I would recomend on not teaching it sand tomb but its your choice. In my opinion just evolve it as early as possible.