I am an Australian aged over 50 and just want a simple explanation of how to get a 90 day tourist visa without all these border runs etc etc.

Can I just apply for a 90 day visa before going to Thailand or is a 60 day visa the most you can get and then have to do a border run for a 30 day extention.

How does that effect me if I purchase a return flight 90 days on from date of entry if I can only get an initial visa for 60 days ?

Is there a simple explanation of these rules somewhere, that can be taken as "gospel"???

Well, I can answer this simply.

Get a tourist visa in Australia. It will allow you a 60 day stay in Thailand. You can get a 30 day extension of that visa at a Thai immigration office in Thailand. You cannot get a 90 day tourist visa in Australia, or anywhere. You must enter Thailand within 90 days of getting your visa, so be sure not to get it too early. With the visa, no worries boarding your flight. Have a nice holiday.

Embassy and even Consulate web sites normally provide a good rundown of various visas. But your question has been answered - you want a tourist visa which provides a 60 day stay that can be extended 30 days for 1,900 baht and photo at an immigration office inside Thailand.