Old and youth exist in our society as a common appearance.
... This is a too obvious idea. You need a line with more punch to start an essay.
In some cultures, old people are more valued, but in other cultures, the youth are more valued.
What's under controversy is that whether old people or youth are more valued
Actually, your prompt does not talk about any controversy. It says that in some cultures the youth are valued more than the old. So, you need to align your sentences with the topic theme. In the introduction you need to introduce your topic to the reader and then state your opinion. Also it's important maintain a proper alignment with your topic throughout your essay.