Konnichiwa Maciamo-san! Dswbg-san!
to Maciamo-san
Who is in a higher position of respect? A 45 year-old female minister? or an unemployed 60 year-old man? It's easy to answer.
Both of them must use Keigo with each other in a case like that. Because the female minister is higher position than unemployed man, but 60 year-old man is older than 45 year-old female.

There is many class in the world. Generally, a 45 year-old female minister is respected from the public more than an unemployed 60 year-old man. But if the unemployed 60 year-old man is senior statesman who live in retirement now? If she had been supported from the senior statesman who was on active? The female minister respect him. The public respect the minister by social reason, but the minister respect the unemployed man by personal reason. Standard of respect is not only one.
And it is not strange in a case like you. You teach English to people who can not speak English. People respect you naturally because you can speak English but people can not speak English. It is no relation to social position, age and nationality.
You wrote explanation sentence about Keigo. It's a very great. But I find only one error. It's a "o-tabe shimasu". Kenjou-go is used in the first person's verb. But Teinei preposition "o" is not in the first person's verb. You must not attach "o" to your own verb in Kenjou-go. "itadakimasu" is good but "o-tabe shimasu" is not.
to Dswbg-san
Polite form is very important in Japan. But I think that you shoud learn normal form perfectly at first. The most important mutter of language is possible to understand each other. Polite form is not so important. In Japan, polite form is very important with the Japanese. But polite form is very difficult even the Japanese. And the Japanese deal leniently with a foreigner's speaking, polite or not. The Japanese never get angry even if you don't know polite form. And you are free from troubled with polite form because many young Japanese can not use polite form correctly.
NANGI