The issue here is when your country first developed as more-or-less recognizably the country it is now. Exclude for the moment violent changes of government, invasions, significant social changes, territorial expansions or contractions, etc.
For some, this would be relatively easy: the USA for instance emerged as a function of the American Revolution. Before the Revolution, there were a bunch of British colonies. After the Revolution, there was a country called the United States. It is true that the US greatly expanded after that, and its nature changed as a result of Civil War and social change, but the country today is still recognizably the same entity.
For others though it will be harder. When did “England” emerge? I read a convincing argument that what we now know of as “England”, although conceived of by Alfred the Great, only truly emerged under his grandson Aethelstan. Before that, there were still various kingdoms within what is now England, of which Alfred was only king of Wessex. No doubt cases can be made for other times.
What about your country?