In Grand Bahamas, his family members were the only whites in an entirely black community, and in Puerto Rico, everyone spoke Spanish.

"My initial attitude was that 'the people on the islands were poor and I am a rich American'. Later, I realized how humiliated I was because I found out that the local people knew more about how to live in difficult conditions than Americans. That's when I knew there is so much to learn beyond American culture."

This epiphany changed his mindset and paved the way toward an easier tenure in Germany and later, China. Dietz believes all cultures are interrelated and regards his stay in Germany as an important stage in his life during which he saw the connection more clearly.

For example, he points out that Georg Hegel's thoughts influenced not only the West but also Russia and China through theories of Karl Marx.

He studied Eastern religions, Chinese philosophy and history after coming to China and regards himself as a student of China that way.

He teaches about 15 hours every week in Yangshuo now, living off his US pension.

Seven years ago, his students were mostly successful businessmen from across the country, who came to improve their English. Now most of the students are younger and from places not far from Yangshuo and they come to learn English to find a job.

He has taught more than 100 students and often goes to Shenzhen, Wenzhou and Shanghai to attend get-togethers organized by his students.

He also trains his students how to teach English. That his students can teach English is the largest reward for him.

"He is very honest and generous. He is like a grandfather to a very large family. He refuses to take our money because he says money ruins the volunteer spirit," says one of his students, a young lady named Sun who is a tour guide in Guilin.

The saddest thing for Dietz was when his wife Joanne died in Yangshuo in 2010 at the age of 83. He grieved for her for nearly two years until he told himself: "I don't like being single".

He found his second wife, Zhang Lianfang, a 63-year-old from Changsha in Hunan province, through a matchmaking website.

Dietz sums up his life in Yangshuo as "been there, done that", but the spritely grandpa volunteer thinks the best is yet to be.