You are not getting an extension. Your are arriving without a visa (or extension) and expecting to get a "Visa Exempt" stamp which is intended for tourist who visit Thailand for a short stay (usually interpreted as 90 days or less. Based on your history of visits to Thailand, Immigration could rightly decide that you are no longer a tourist and refuse to give you the stamkp, effectively denying you entry. If you want to spend more time inThailand without being denied entry you need to get a visa.
It sounds like you have a solid history of visiting Thailand using the Visa Exempt entry. If so, Immigration may consider that you are abusing the system which is intended for sshort term tourism. You may get denied entry unless you arrive with a long term visa suited to the reson for staying in Thailand.
Zoe Zhao. I have no idea who you are or where you come from. Nor am I interested in noing. But it seems to me that you are trying to get a job with the Immigration Police. Unbtil then, what people do is not your concerm.
To get a Retirement visa in Thailand you need to have the money in a Thai bank account. It is not possible to open a Thai bank account on a 60 day visa free entry or on a tourist visa, only on a long ter, visa. Best get a Retirement visa in your home country, then you can open a bank account once you are in Thailand.
Your Retirement Visa rann out on its date of expiry. If you have been here for 18 months, then I assume that you are currently on an extension of stay based on being over 50 and not a Retirement Visa.