Just so we're clear
@Al**
, there is NO such thing as a retirement visa. Not gotten inside the country at the immigration office, not gotten at a thai consulate out side the country. Unfortunately, calling it a retirement visa by every Tom Dick and Somchai thai official and foreigner alike doesn't mean that's what it is :/
As has been pointed out this is a 90 day Non-Immigrant Type O visa issued based on the fact the holder is over 50. It costs 2000baht and can be gotten if you meet the requirements and have 15 days or more left on a 30 day visa exempt stamp or a 60 day tourist visa stamp
The ONLY place the word retirement appears is that stamp in engrish they put in your passport.
The actual clause that visa is issued for is in Police Order
********
clause 2.22 which states in thai
กรณีใช้ชีวิตในบั้นปลาย <- in the instance of living out the end of your life :O
Don't forget getting this visa is just the first step toward getting a yearly extension of stay based on being over 50. Once you are down to about 30 days or less left on your 90 day stamp you go back and apply for the yearly extension of stay for 1900baht.