depending on how you define democracy.

This part of your comment seems to be doing a lot of heavy lifting.

According to the ancient manuscript Landnámabók, the settlement of Iceland began in 874 AD, when the Norwegian chieftain Ingólfr Arnarson became the island's first permanent settler.[15] In the following centuries, Norwegians, and to a lesser extent other Scandinavians, immigrated to Iceland, bringing with them thralls (i.e., slaves or serfs) of Gaelic origin. The island was governed as an independent commonwealth under the native parliament, the Althing, one of the world's oldest functioning legislative assemblies. After a period of civil strife, Iceland acceded to Norwegian rule in the 13th century. In 1397, Iceland followed Norway's integration into the Kalmar Union along with the kingdoms of Denmark and Sweden, coming under de facto Danish rule upon its dissolution in 1523. The Danish kingdom introduced Lutheranism by force in 1550,[16] and the Treaty of Kiel formally ceded Iceland to Denmark in 1814.

Influenced by ideals of nationalism after the French Revolution, Iceland's struggle for independence took form and culminated in the Danish–Icelandic Act of Union in 1918, with the establishment of the Kingdom of Iceland, sharing through a personal union the incumbent monarch of Denmark. During the occupation of Denmark in World War II, Iceland voted overwhelmingly to become a republic in 1944, ending the remaining formal ties to Denmark. Although the Althing was suspended from 1799 to 1845, Iceland nevertheless has a claim to sustaining one of the world's longest-running parliaments. Until the 20th century, Iceland relied largely on subsistence fishing and agriculture. Industrialization of the fisheries and Marshall Plan aid after World War II brought prosperity, and Iceland became one of the world's wealthiest and most developed nations. In 1950, Iceland joined the Council of Europe.[17] In 1994 it became a part of the European Economic Area, further diversifying its economy into sectors such as finance, biotechnology, and manufacturing.

https://en.wikipedia.org/wiki/Iceland

And how you define nation/country. You could say the Isle of Mann, but it probably doesn't meet the definition.

The post doesn't say existing nations, it says there has never been one longer than 250 years.

When Greeks invented the term they stipulated only free men were able to vote. So depending on how you want to look at it, any country that allows free men to vote is a democracy. We've (modern people) just updated the terms of service to suit our current version of morality. We might decide our thinking outdated and misguided in the next 250 years and change things again. Hell we might even give trans people, women and people of colour equal rights to white men, you know, like legal protections and such. We might not try to suppress their votes... idk has anything actually changed since 1964 or did Americans just visit the moon?

In that case there wasn't any democracy up until maybe 100 years ago (no clue what country first ticked all the boxes, or when)

It wasn't one back then either. Women and black people weren't allowed to vote from the start.