Middle Chinese

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(1) Old Chinese and Middle Chinese is about phonology (pronunciation), not literary style (both are Classical Chinese 文言文, which was spoken Chinese "from the end of the Spring and Autumn period (early 5th century BC) to the end of the Han dynasty (AD 220)" en.wikipedia.org for "Classical Chinese")

(2) Chinese language history is generally split into three phases: (1) Old Chinese, the form of the Chinese language SPOKEN between the 18th century BCE and the 3rd century CE; (2) Middle Chinese, between the 4th century CE to around the 12th century CE; and (3) Modern Chinese, since the 13th century.

(3) Pronunciation of Middle Chinese is largely reconstructed based on the book Qieyun 切韵.
https://zh.wikipedia.org/zh-cn/切韻

(4) Chinese language
https://en.wikipedia.org/wiki/Chinese_language
("Currently, most classifications posit 7 to 13 main regional groups based on phonetic developments from Middle Chinese, of which the most spoken by far is Mandarin (with about 800 million speakers, or 66%), followed by Min (75 million, e.g. Southern Min), Wu (74 million, e.g. Shanghainese), and Yue (68 million, e.g. Cantonese)" )

Take notice that all current regional groups of Chinese are descendants of Middle Chinese, in terms of pronunciations.

(5) Gary Lee, Cantonese FAQs. undated
https://www.ocf.berkeley.edu/~garykl/cantonese_faqs.htm
("Q: Is Cantonese closer to Middle or Old Chinese than Mandarin?
A: The general answer is NO, since both languages have undergone a lot of change. Phonetically speaking, certain aspects of the Cantonese sound system have undergone less changes than Mandarin has, so in those respects, it would be closer. Nevertheless, Middle Chinese pronunciation is still a long way from Cantonese pronunciation. Certain vocabulary has been preserved, while others have not. Grammatically, there are definitely differences. If you traced the two dialects back to Middle Chinese, you will find that both have undergone significant change")

Gary Lee described himself this way:
"What I currently do[:] I'm a part of the support staff at the Oakland Public Library in the Computer Services department. * * *
What I’ve done previously[:] I was the UC Berkeley Cantonese Decal (student-run courses) facilitator, instructor, and webmaster from 2005-2007. With the assistance of many  wonderful student instructors and assistants, we taught the Cantonese language to fellow students. Find out more by going to my Languages page."