One month before your visa expires, you should file for an extension. Please check with your local immigration office for further information on when you may request for an extension. ”
As long as you've been granted permission to remain, you may seek for an extension. Even if your application is complete, you should submit it a few days before the expiration date in case you need to supply extra documentation.
As with the Non-Immigrant O visa, you must complete a TM7 Extension of Stay form to achieve this. This time, you must establish that you have at least 800,000 Thai Baht in your Thai bank account (or in your country of residency if you apply in that country), 65,000 Thai Baht each month in your bank account, or a combination of the two that totals at least 800,000 Thai Baht.
If you are extending on top of a OA visa then you will need to have a Health Insurance policy which meets the visa requirements. You can see an example of one of these policies below.
Yes, this is a common option provided by visa agents.
For example Thai Visa Centre offers yearly Retirement Visa Extension services starting at 14,000 THB.
If this is something you need you can message them over their 24/7 @LINE Support Account.