My wife and I (both Americans over 50) are on ED study visas for more than one year. We want to change to retirement visas when our extension is up in September. Can I the husband (57) file for retirement and have my wife (51) as dependent on US$25K (800,000 ? I don't want to have to show 2 x $25K ($50K). As Americans, is the US consulate affidavit for income verification adequate for the application if I show $25K/year income? Or do I need something else? Where do we do the criminal check, and medical check since we already live here? Thanks.

If 25k USD equals 65k Baht when you extend, that is all you'll need. The letter is acceptable.

No medical or police check needed for extensions. They are only needed if applying for An O-A Visa in your home country.

You need to show a monthly income in dollars on the affidavit which at 32 baht to the dollar is about $2031 per month so 25K annual income would be more than enough,

Your wife can get an extension of stay as your dependent with no additional financial proof needed.

When you change the reason for your extensions of stay to retirement/dependent you will need a letter from the school stating that you are no longer enrolled in the school with an effective date no later than the date you apply for the extensions..

Thanks very much. When I go to immigration, do I just say "retirement visa" or "changing from ED to retirement visa"?

There is no retirement visa done at immigration. You will be applying for an extension stay based upon retirement. Your wife will be applying for a dependent extension of stay.

You both will need to fill out a Extension of Temporary Stay in The Kingdom Application Form (TM. 7) (print two sided) and attach a photo.