This is Lumos job!
It may well be semantics, but there is no such animal as a "retirement visa".
Yes, Pagey, there is a difference. With 0-A you basically have to prove your case with different requirements before you arrive in Thailand, the advantage being that you will get 12 months on arrival if you have one.
With a plain non immigrant "O" visa it can be either multiple entry or single, you get 90 days, after which time you have to either exit, or apply for an extension based on retirement. You will then only have to prove either 800k Baht in a Thai Bank, OR, 65k Baht / month, or a combination of the two that equals 800k. For the first extension the 800k has to be in the Bank for a minimum of 60 days, the next year 90 days.
I am sure Lumo will be along with his good advice soon, but that may help you for now.
