I feel like grandparents are supposed to die
Do you feel sad about that?
Not really because my grandmother died when I was young.
Death is a thing that everyone experiences eventually. There is nothing wrong with understanding this fact and thinking about it.
I think old people sucks and their purpose is to die.
Old people will die, it's a fact of life. But while they are alive their lives are still meaningful. I suggest you spend some time with the elderly to appreciate them more.