...actually it's a bit more objective than that.
They have to reach the required comeptencies in the syllabus and that takes as long as it takes, so rather than using the old "would you send your family" etc you actaully have a measurable bit of evidence that they are ready.
I also got taken to task by CASA for not sending them as soon as they were competent and moving on to other bits of the syllabus instead. I had to explain that the delay was actually in waiting for the wheels in Canberra to grind around and produce the student licence, ASIC and medical...things that used to be done by the CFI and the DAME and took minutes rather than months...