* Stories that were written down first? If so, then the answer is likely ancient Mesopotamia and Egypt. These civilizations developed writing systems thousands of years ago and left behind a wealth of literary texts, including epic poems, myths, and historical accounts.
* Stories that have been passed down orally for the longest time? This is much harder to pin down. Oral traditions can exist for thousands of years before being written down. Many cultures around the world, including Indigenous communities, have ancient oral traditions that are likely much older than any written text.
* Stories that are still popular today? This is a different question entirely. Many ancient stories, like myths and folktales, have been adapted and re-told throughout history, and continue to be popular today.
To give you a more specific answer, could you please clarify what you mean by "oldest stories"?