@Lynne ******
You cannot get an O-A VISA from inside of thailand. You get that from the thai consulate in your country.
You are talking about applying for a yearly extension of stay from the immigration office that serves the area where you live.
I'd say about a month or so before your current Non-O entry stamp expires go to the immigration office and get the hand out that lists the requirements for getting a yearly extension based on being over 50 (retirement)
If you have more questions you need to open your own topic..
Good Luck