I can't fully understnd this sentence

[chertopert]

Please read the following paragraph and pay attention to the first sentence:

Throughout history, the difference between the old and the young has been a defining feature of both reality and literature. Parents have power over their children … but as those children get older, they begin to put pressure on their parents’ power. They test the rules; they rebel; they create their own rules. The parents are puzzled, disappointed and angry about the shift in the balance of power.

What does the first sentence mean exactly? How is the difference a feature of reality and literature? Does it mean that writers are writing about the difference in their books (literature)? Does it mean film producers are making reality productions about it (reality shows)?
Could someone explain the first sentence?

[IndiaWalla]

It means that, through all ages there has been no difference in understanding the relation between parents and their children, it's agreed in reality and even in fiction books all authors who write about that relation they present it as has been explained in the article (the first lines).
Bottom line: there is a census regarding the understanding of the relation between parents and their children through all ages, being in reality or in the literature books (fictions).