Well, I sure don't know much. I do know that Australia severely limits the number of adoptions it allows per year. Regarding China, as of May 1st, singles may no longer adopt from China. I know that Vietnam recently reopened for adoptions, and many people--including singles--are flocking there. I know less about Thailand and Cambodia, but a web search might help you get some basic information. Hopefully, someone here will know more.
I would advise you of one thing. If you read about an agency that has limits that disqualify you (such as age), check around for other agencies that may not be as restrictive. I know many agencies pass off their own rules as a country's rules. I just hope that in Australia, you have a choice of agencies.
Good luck to you and keep us informed as you go along. We may all learn in the process since it's different adopting from the US and from Australia.