Unfortunately there are no standard answers to your questions BF5.
The recruitment policies (hold file, review process, etc , etc) can vary depending on who is in charge at the time. Pretty much the only constant is that a fail of the written tests (including psych) will shut the gates in front of you.
The hold file has historically been a bizarre piece of work. Once the policy was a 'ranking system' which allowed people to leapfrog you if they did better at the testing/sim/interview. Then that was scrapped and went to some sort of date based ranking. Then there was a review board which kicked in if you'd been on the hold file for x amount of time and could recommend you either stay on the hold file or get the 'don't bother us anymore, have a nice life' letter. Then that got scrapped. And god only knows what it is now.
Age is not legally a factor (iaw anti-discrimination laws), but the basic premis is 'flying experience for age', so if you're 35 with a few thousand multi hours, you have a chance. Similarly, if you're 40 and have just attained your CPL on a single comanche, they won't deem you competitive!
It's pretty rare, but 3 or 4 people I know have apparently been rejected at interview and have had two bites at the cherry (another interview in a couple of cases). I don't know the exact circumstances, except that some post-interview doubt must've existed. They were pretty good blokes & I'm not sure why they would've been marginal in the first place. Qantas never, to my knowledge, gives anyone more than two chances at anything (including promotion).