Cant answer the recruiting question. If they thought 48 was too old they wouldn't recruit you.
Current projections for command are 12-14 years. So that would put you at 60+. As a new joiner you will have RA65 so now worries on that one.
Cathay will get you closer to home...if you can join as a DEFO you can pretty much stay in Oz until a hkg command comes up...but as I said, that will be around 60-62 if you are keen! If you don't get a DEFO position but joined in HKG you could commute but the salary for SO is pretty bad.
EK - much harder to commute adn much further. Time to command is 3-5 years and expected to be around the same for the foreseeable future.
SO if its command/money you want, EK. If its Australia you want, CX. I am assuming you considered all the aussie options J*,
VB etc