You can probably get assessed for the pension at 67 (if your 61 now), in fact you can start the to apply earlier than your 67th birthday! (Around 8 weeks earlier).
Best you look up the official Oz Govt websites or this place has a free check about eligibility etc,
Hard to definitively answer you cause you don’t mention what visa you are on but if it’s say an O-A year then you should make sure where you are staying makes a report (TM30) and then do your 1st 90 day report in person at Immigration. After that 1st 90 day report, you can then do future reports online.
Maybe you should get legally married here in Thailand before you leave. Then you can return more easily, get an O visa and eventually get an extension based on marriage for a year (400,000 baht in a thai bank).....few other ways too. Goodluck 😄
Oz Ambassador’s next message will be interesting! Hope there’s no reductions with the recent announcement by the PM cutting numbers flying back to NSW, QLD & WA till mid Feb at least.