Is there an age requirement for ESL teachers? Are there any positions open for recently retired ESL teachers?

Not typically but sometimes. China, for example, has a mandatory retirement age (which means that you wouldn't be able to legally work / apply for a work visa after a certain age).

Most countries in Africa have volunteer-based positions and, therefore, no age restriction (on the upper end at least).

Costa Rica might actually be your best bet. Then again, I'm a little biased -- I taught there and loved it :)

Not sure about Dubai.

Also, a potentially useful article for you: https://www.gooverseas.com/blog/best-countries-for-seniors-to-teach-english-abroad