Hey.
regarding your questions:
1) I think the process was described in this thread before so have a look
2) I believe it highly depends on your group. From my 1st stage out of 20 or 25 people only 2 passed, while on my friend’s first day about 10 or more made it through to the 2nd stage.
3) there’s a relative wide age & background spectrum on the course: from 18 or 19yo straight out of high school to folks in their mid 30s. Most of cadets have a degree (at least in the first two groups) often science or engineering related, however guys who joined straight out of high school are doing as well if not better.
hope that helps,
regards,
TL