yep, your belief is in error
@Ma**
, it works like this, IF you enter on an O-A visa you have to get at least 1 yearly extension based on the reason you got the visa (being over 50 aka retirement) by meeting the requirements (proof of funds & proof of insurance by one of the 14 thai carriers).
BUT
If you're married to a thai, after that you can change the reason you're applying for an extension to marriage to a thai when you would meeting the financial requirements of that extension and when you would not need insurance.