Pedro Gunmetal - The Non Imm O Visa Multi-Entry One Year Visa for being age 50 or over - with no financial requirements - used to be issued worldwide prior to early 2016. After that is was no longer issued except for reasons unknown it was still being issued in the UK until very recently. No longer however.
You can still get a Non Imm O Single Entry 90 days - usually however it is now issued as a prelude to using it to file a One year Extension of Stay based on being age 50 or over "retired". If you do not follow through and get the Extension of Stay you will not likely be able to get another one back to back.
Much of this debate about whether a Non Imm O-A Visa can be extended one year based on Marriage or not is complicated and confused by the typical culprit. That is - the culprit is the near total lack of Consistency from one Imm. Office to another Imm. Office on rules, orders and policies. There are neatly up to 75 possible interpretations of any police order or policy on any given day. So it seems to me that it is very possible that one Imm. Office decides to extend an O-A for Marriage. Why Not? There are dozens of different interpretations of various police orders happening every day.
In the future with Non Imm O-A Visas requiring health insurance... And in the future - upon finishing the 2 years of stay... an O-A Visa holder might be require to still maintain health insurance coverage upon applying for an One Year Extension of Stay. In that case one scenario would seem possible - that an Expat (former O-A Visa holder) could just go to a Thai Consulate in a Thailand neighbor country (or region) and get a Non Imm O 90 days, then enter Thailand with the Single Entry Non O and apply for an Extension of Stay at the 30-45 day mark (assuming the Expat has the required financial credentials)... Immigration I/Os might wrinkle their nose but may well approve it.
Non Imm O-A Visas CAN be Extended at Immigration for One Year. It works like this. An Expat has an O-A Visa obtained in his/her home country. The 2nd Year Permission to Stay is acquired by exiting and reentering Thailand near the First Year Expiry Date. Some few Expats holding O-A Visas do not want to do a Border Run / Bounce or don't realize it is available. So they just go to their local Immigration Office and apply for an One Year Extension of Stay. I know this happens because I have read many accounts of this happening successfully. Or in the other hand the O-A holder obtains the 2nd year of permission to stay with a Border Bounce. Then towards the end of the 2nd year they go to the Local Immigration Office and apply for a One year Extension of Stay. I know this happens because I have read many accounts that it happens routinely. Whoever says this can't be done is just flat out wrong.
Notice the new requirement that those people age 50 or over who are on a one year Extension of Stay based on an original O Visa in the past... Are now required to not allow their banked money to fall below 400,000 Baht. Now compare that to a Non Imm O-A Visa holder (age 50 or older) who does not have to keep 400,000 Baht in the bank... But has to have Health Insurance covering a 400,000 Baht hospital bill. Now see the reason for the matching 400,000 figure?