What are the requirements and processes for obtaining a Non-O visa for retirement in Thailand?

Better to start with the non o in your country rather than a tourist visa. The bank account will be easier.

Q1- Do you have to be 50 years old to apply for the initial Non O Visa or just to apply for the extension?

-> You need to be 50 years old as of the application date for the initial Non-O visa based on retirement.

Q2- Lenght of stay

So is it 90 days (original visa) + 1 year (extension) from the entrance date in Thai OR 1 year (if you get the extension) from the entrance date in Thai?

-> You will be stamped in for 90 days starting on arrival day. You will apply for a 1-year extension before this first 90-day is up. Once the extension application is approved, 1 year (12 months) of extension is added to your stamp.

Q3- Renewal

This is what i don’t understand: so once you finish your legal length of stay…you just apply for a new extension of the original Non O visa over and over again year after year? With no limit?

-> You apply for a new 1-year extension every time before your stamp expires. No limit as long as you meet the requirements.

Q4 - Re entry permit

So you first apply (and obtain) the Non O Visa and then ask for a re entry permit at the airport every time you want to leave right?

-> Re-entry permit has two types, single re-entry or multiple re-entry. Both would be the same expiry date as your latest permitted-to-stay (entry or extension) stamp.

If you travel often, you can get multiple re-entry permit once for unlimited travel for the whole extension period.

Re-entry permit application can be done at the local immigration office anytime or at the international airport when you travel out from Thailand.