Just thought I would clarify a bit further. There are always ages and time-since-transitions present for all probabilistic transitions in both Path and VDDT. As Randy points out, the toggle on the Probabilistic Transition screen simply shows/hides these columns in the display – the underlying values for these columns are still present and used by the model even when not displayed. Note, however, that when a new transition is created, the default values for ages and time-since-transitions are set in such a way that they have no effect on the model predictions – for example the minimum time-since-transition value is always set to 0 by default. The result of this is that if you don’t ever use (or display) the age and time-since-transition columns, the model will still run as though these features were not turned on.
Hope this helps – Colin.