What are the requirements for extending an O-A visa in Thailand?

It may be prudent to apply up to 30 days before the expiration date. You still get the years extension but this allows you to work out any details vs trying to do so a day or so before expiration.

Hi Eric just a question, have you had your 2nd year stamp on the OA purchased in your home country? Is this for a new year?

Just so you know you can make an appointment at C/W for a new retirement extension and then just show up 10 minutes before that time and jump the whole queue :O

Here's the link

You are confusing the requirements to BUY an O-A visa from a thai consulate in your country with the requirements to get a year extension of stay from the immigration office inside the country.

There is no medical certificate or background check required when applying for a year extension.

If you're using the 800K baht banked money you need the funds in your account for 2 months on the date you apply for your extension (not when your current stamp expires). You need to have the insurance from one of the 13 approved thai insurance companies (Pacific Cross is one of those) and you need to have the rest of the required documentation listed on that sheet.