The US lasted 243 years. Is it the oldest modern nation? I wonder, how will the modern nations different from the ancient ones?
Edit: Seems that GP conflates "nation" and "state". If we're counting continuity of government, they probably only Great Britain is a good example, other countries had undergone many changes, from absolutism, to constitutional monarchy, to non-existence, to democracy, to fascist dictatorships.
Sure they're still Britain but it changed a lot. (it also apply to France, Germany, Belgium, and probably a lot more)
However, the lineage of the what is now the UK does stretch back in places over a thousand years to the creation of Scotland and England as separate unified kingdoms in the 9th & 10th centuries.
https://en.wikipedia.org/wiki/List_of_sovereign_states_by_da...