Starwood and Plum aren't available here. Plum DOES run superannuation funds here though.
Black credit is what we have in place of Plum.
In place of Starwood, well, there are a few programs, like Virgin Velocity if you have Virgin credit... But the interest rates with Virgin are insane.
Hoyts, you're not going to be able to get anything other than a basic credit card, unless you've been paying bills in your own name for a while and therefore have a credit score. It's not about age, so much as being able to prove a reliable income income and that you pay your bills on time.
I had a job as well as my own mobile and internet bill that I was paying from 16, paying by Bpay the day I got them. When I was 18, I was already eligible for a gold card (sadly, so are my pets thanks to the way my vet bills me).
Keep up a good score on the gold, pay your bills regularly, keep cash coming into the account that's linked to the card, and you'll be pre-approved for platinum soon enough, and then black if you start doing 6 figures a year.
Piece of advice for another Aussie. Get an account with St.George. The branches are a pain in the arse to find, but they do have the best credit cards on the market. They don't have fancy crap you'll never use, like an RFID tag to wave at a cash register. They just have an interest rate about 3% below the market average and lower annual fees.