TQ, you can't fly the 744 over the age of 60 due to the fact that most nations won't allow you to fly in their airspace as pilot in command over that age. What a few (and increasing) of our 59 year olds do is bid back to the 767. Australia has no such problems and so due to the high domestic workload on the 767, they can happily sit on the top of the seniority pile, pick the eyes out of the best domestic trips, get the best leave slots. Of course, if heaven forbid they actually get nabbed for a standby, they won't be assigned a trip that takes them to/through Indonesia or the USA. That basically rights off any flight north of PNG. They can do Tasmans (I think) and domestic and thats about it. It is a source of some contention with both sides of the coin having strong views about it.
A 'squirrel cage' is a way or organising the rostering system. When you change onto that type, you start at the bottom of the seniorority pile and basically get what is left over of the trips that have been allocated. As the months progress, you move up the pile until you end up at the top and get whatever you want (thats the theory anyway). After that month you drop to the bottom again. Pretty fair and equitable all things considered. Why doesn't the 767 have that I hear you ask? Because the 'cage' was one of the post dispute things and to implement it now on 767 significantly disadvantages those who have been on the aeroplane for six years and suffered being on the bottom of the pile for the first three of those six years. It is equally 'unfair' to now drop them to the bottom again having done THY (the hard yards) as a junior person on the seniorority pile.
This is the reason you see the 744 drivers coming to the 767 and not the 737. They will ALWAYS be senior on the 767- unless something changes.
A couple of things from the 'anti' over 60 side. It means that they are holding up promotion of F/Os to Captain and S/Os to F/O. They don't care (and I don't mean that maliciously) because they are looking out for number one- and keep extolling the rest of us to do the same. It also means that it places extra restrictions on the rostering side of things. They can't be 'turned around' in Melbourne the same as other crew and sent to Singapore or Hong Kong or Japan if another Captain goes sick and so that doesn't make it the 'equitable' system that seniorority is supposed to be. There are a couple of other issues associated with it as well but I've already stuck my head a long way above the trench on this one and will leave it there for the time being. No doubt, someone, somewhere will take note of my comments and line me up. Interestingly, for me, it ain't personal, its just how I feel although some who are more sensitive seem to take any disagreement with them on this issue personally. Ironically, it is exactly the same to how they feel about extending. It ain't personal about someone not getting their promotion, it's just how they feel.
Hope that clarifies.