I've met a few Jetstar Cadets and they didn't appear to be 18yo school leavers.
The most impressive Jetstar Cadet I met was late 20's and his first career was as a builder. He stood out from the crowd by working hard and being more prepared.
From memory, 7 out of 9 J* Cadets who started the course completed it, which is a much higher completion rate than other integrated courses. It probably means the selection process works well and picks up the right ones.
The J* Cadets seemed generally happy with their course, but did complain about OAA/CAE being disorganised and they thought the Virgin Cadetship might have been better.