What are classical languages? How they are different from other languages? Is English is an example of classical language?
The Wikipedia article is a good reference.
A Classical language should be ancient, it should be an independent tradition that arose mostly on its own, not as an offshoot of another tradition, and it must have a large and extremely rich body of ancient literature
Is English is an example of classical language.
In the context of traditional European Classical studies, the "Classical Languages" refer to Ancient Greek and Latin. In terms of worldwide cultural importance, Edward Sapir in Language (1921) would extend the list by Chinese, Arabic, and Sanskrit.
However, it also states
Early Modern English (language of KJV Bible and Shakespeare, 16th to 17th c.) is the classical stage of English -
Such a stage is limited in time, and is considered "classical" if it comes to be regarded as a literary "golden age" retrospectively
This means today you would consider the Shakespearean period to be the golden age of the English language.