@Jamie *******
The poster is getting a "Zero-entry Non-O Visa Based on Being Over 50", which is valid for 3 months.
He *CAN* apply for a One Year Extension of Stay Based on Retirement when he has 30 days or less remaining (45 days at some immigration offices) on his existing "admitted to" stamp from the Non-O Visa.
Once he gets the Extension of Stay, he can apply for a Single or Multiple Re-entry Permit at any immigration office for 1K THB/ 3,800 THB.
The problem with that strategy though is the money. He will have to keep the 800K THB in a Thai bank account for 2 months BEFORE applying for the Extension of Stay, 3 months AFTER getting the Extension of Stay, and not having the balance dropping below 400K THB during the in-between period.
That is a valid option if he's willing to keep the money seasoned in the bank though.