I have two 25" silvers, one I adopted at 21" and it already had DE in one eye. The other silver I raised from 3" to 18" without DE. After a violent collision into the side of the tank while I was trying to catch her for tansfer to another tank she developed DE. Six months later at 24" she had another collision with the top of the tank during a water change, she the developed DE in her other eye also.
In both cases the DE developed within a few hours after each collision.