Why should we value elders?

Because, young man.
Elders can't really do much because their ability to do everyday things is simply restricted because of old age
Also respecting someone older than you is basic equette or being polite.
Which basically means if you disrespect someone older than you, you sir are being unpolite or rude. Well except if the elder is being rude for no reason then I guess it's allowed for you to be rude back.
So basically, RESPECT YOUR ELDERS.

That's it.